making thin sections by hand

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MAKING THIN SECTIONS BY HAND

Richard Hill

Email:[email protected]

Published by the Mid-America Paleontology Soc. in the Expo proceedings for 1999.

Abstract

A method of manually making thin sections is presented. Simple

techniques for maintaining parallelism that avoids direct measurement

is described in detail and a number of examples are shown.

Introduction

Most amateur paleontologists never bother to look at their specimenswith a magnifying glass let alone a microscope. They do not notice the

detail available in most fossils and the abundance of microscopic flora

and fauna that exists at this scale. These microfossils can beindividual tiny fauna, juvenile live stages of larger fauna, or parts

of larger fauna. Soft shales and friable limestones offeropportunities to free microfossils from matrix without resorting to

drastic chemical methods, but too often the microfossil hunter comesacross exquisite fossils in glass hard matrix. In such cases the

difference in hardness between fossil and matrix is usually so close

that there seems no way to free and exhibit the fossils. Thinsectioning these hard rocks is a means to not only enjoy these fossils,

but in many of cases may be the only means of accurately classifyingthe fossils. This can lead the amateur paleontologist on an exploration

in the microstructure of some of the largest megafossils. (Jones

1956)

The techniques described here are simple but can lead to remarkableresults. This was gleaned from several sources and tried over the last

few years. (Allman & Lawrence 1982, Kummel & Raup 1965) Patience isrequired for rushing the job will inevitably lead to ruin of the

specimen and a waste of the time put in to the work. Materials, for themost resourceful amateur, can literally cost nothing and at most will

cost little.

Procedure Overview.

The task is to find a good specimen, grind and polish one face of a

small cut out slab, glue that to a glass slide. Next, grind down andpolish the other face of the specimen so that it is parallel to the

first side and only about 0.03-0.05mm thick.

Finding a specimen.

Check the matrix around some of your fossils and you will likely find

pill-shaped, torpedo-shaped and round inclusions. If you are lucky andthe formation is rich, you may find identifiable fossils that are

smaller (juvenile) versions of the megafossils. In the field you might

find a rock that looks for all the world like a collection of sphericalor cigar shaped grains. If you know the matrix to contain abundant

megafossils then it is likely full of microfossils and you would dowell to bring back a rock of the material. Many is the time I found a

rock that only looked mildly promising and upon making the thin section
mailto:[email protected]:[email protected]


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found it to be abundantly rich in fauna. I have yet to find apromising rock that proved to be uninteresting.

Cutting the specimen out.

Back in the lab (read garage or basement!) cut off a piece of one end

of the rock. The harder the rock the better. You don't want itcrumbling. (We will deal with the crumbly ones later.) You do not need

to cut off more than a one inch square piece and would be better off ifit were less for a first effort. If you do not have a motorized saw, a

simple hack saw should do well. Cut another piece off the main rock as

thin as you can, 2-4mm will do but 1- 2mm is better. If it breaks thensave the pieces. The important part is that you have a little slab with

roughly flat, parallel sides under 1 square inch area.

Materials for grinding.

For the next steps a selection of grinding powders will be needed

along with some other items:

220 carborundum or silicon carbide400, 600 carbo. or silicon carbide or F and 4F pumice powder

5 micron (fining powder) or equivalentCerium polishing powder

A piece of twill or denim.

Microscope slides.Epoxy (20 min. or longer) or PaleoBond glues.

Some pieces of brass shim stock or equivalent, preferably in severalthicknesses and at least twice as long as the narrowest dimension

of the microscope slides being used.

More of the coarse powders will be needed and less of the fine which

should please your wallet. These can be found at most any rock shop.There is no need to buy better grades and these are only

recommendations. Substitutions can be made as to powder composition andgrade. At minimum a coarse, medium and fine grade is required. Diamond

polishing paste while not only expensive is too hard for this work.Titanium oxide is too slow and soft. Cerium offers a good compromise

and is a very fast polisher especially if attention is paid to the last

grinding step to make sure it is "fined" thoroughly.

Grinding tools.

You will also need some glass blanks. The glass should be at least

1/4" thick and about 4" round or square. If they are three inches thatwill work but the work will go a bit slower. If the blanks are square

and you have a glass cutter, it is advisable to cut off the corners

thus making an octagon. Be sure to grind off all sharp edges with awhetstone or a fine grinding stone on a grinder. This will save you a

bloody mess should you slip when grinding. The glass will likely notbe truly flat when you get or cut them. Check them by bouncing light

off the surface at a very low angle look to see if any light passesunder the edge of a ruler laid across it on edge (see diagram at end of

paper). Make sure it is a good quality ruler (available at good

hardware stores). Ideally, if the glass is dead flat, no light will be seenbelow the ruler especially after the glass is ground a bit. Anywhere a thin

thread of light can be seen is a low spot. With a freshly cut piece ofglass it is probable that the very edge will be higher than the middle.

This is due to a problem called the Twyman Effect. There is a lot oftension stored in a polished glass surface and when it is cut the

surface of the glass relaxes almost always resulting in a

"turned-up-edge". This can be ground off easily using the instructionsbelow.

Truing the glass blanks.

Glass blanks can be brought into flatness by grinding several againsteach other. This is an old technique used by opticians for several

centuries. (Since I have been grinding telescope optics since 1965,


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this was "old-hat" to me.) To start take two of the glass disks and putone on some newspaper on a good flat surface. I prefer working in an

old baking pan or cafeteria tray to confine the slopped abrasive andrun-off water. To begin a "wet" put a "charge" of the 220 grit on the

bottom glass disk with a little water. Grind another similar sized disk

on top back and forth with a stroke that causes and overlap of about aquarter of the disk diameter. Keep rotating the top piece every few

strokes and the bottom piece, in the opposite direction, every minuteor so. As you grind the top piece will become concave and the bottom

convex. So if you started with a piece that was ground down in thecenter and thus concave and put that down as the bottom piece,

eventually it will be flat again by this process. You will have to

check with the ruler every few minutes. To make them initially flatshould only take five to ten minutes.

If you are working only one specimen initially, have the

turned-up-edge problem and the specimen is fairly thick piece of rock(in the 4mm range) you could just grind in a circular motion around the

edge of the blank for the coarsest grade and check it afterwards. It

will probably then be pretty flat by then.

Grinding.

It is useful to define two terms here. Grinding is where a looseabrasive will be used between two unyielding surfaces, as in the case

of rock and a piece of glass. It can also be where the abrasive is held

by an unyielding medium like with diamond and carborundum grinders andgrinding wheels. Polishing, on the other hand, is where the abrasive is

held by a softer yielding medium and it scours the object pushedagainst it. In polishing there is also an micro-melting effect, but it

is not necessary to go into that here.

Take the little slab, place it on the glass tool with some abrasive

and water from a rinse water bowl or pan that you should have nearby.Use only one finger on the back of the piece and grind with a medium to

light pressure and move in a zig-zag or circular (epicycular) motionaround the glass tool (see diagram at end of paper). Be sure to move

about the glass plate as best you can so you don't grind a low spot inone area unless you are trying to grind down a specific area of the

tool (as in the example mentioned above). Grind it until all the saw

marks are gone. Use a 10x handlens to inspect the piece as you grindit. If you had a steady hand on the saw and the cut marks have little

relief, you could start with the 400/600 abrasive size. After each

abrasive be sure to inspect the surface to see if the pits left by theabrasive are uniform and that all the bigger pits from the previousabrasive have been removed. Be sure to wash up the work completely

between abrasive. One grain of a coarser grit in the finer grades willruin your hard work. All this is particularly important if you are only

using the three minimum grades of abrasive for grinding. I use the

cafeteria tray with newspaper in the bottom and toss out the paperafter every grade plus wash the tools, specimens, and change the rinse

water.

Once all the saw marks have been ground off the specimen and you aresure on inspection that the piece is still flat and the grind pattern

on the plate is even, you can go on to the next abrasive. I go

straight from 220 to 400 and then 5 micron. This is the minimum amountof steps you should use but you can omit the 220 if the original saw

cut is smooth enough.

Again push the piece around in the abrasive with a medium to lightpressure. Don't rush the grinding or you will break the specimen. If in

the finest stage the piece kicks and sticks, try using a thicker slurry

of abrasive and less pressure. If it still sticks you may want to washit off and check the glass blank to see that it is still flat. If the

rock is concave and the blank a flatter curve the work will kick andstick badly. It is unlikely that this will be a problem with a first

piece done alone but may if you do a few at a time. In order to have aproblem with this you would have to be a few hundredths of a millimeter

out of flatness so it is advisable to only do a couple pieces at atime. If you do have to re-true the tool, be sure to do a minute or

two of grinding with the previous abrasive to make the specimen match


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the new curve of the tool.

Polishing.

We now need that yielding medium to hold our cerium polishing compound.It also needs to be firm enough to not change the shape of the ground

surface of the specimen. Go to your household rag-bag and get a pieceof twill (from and old pair of workpants) or denim. The piece needs to

be only half again longer than the diameter of the glass tool and halfas wide. Get it wet and wrap it as tightly as possible around the

glass tool. This is tricky but not impossible. The object is now to

put some cerium polishing compound on the cloth and rub the groundsurface over the cloth so it does not bunch or catch on the specimen.

This may take some practice. You need not work it in one of theaforementioned patterns as we are now not wearing down the glass tool.

Just rub it back and forth on the cerium charged cloth until you get agood polish. If you want to spend the money there are supply houses

that carry self-adhesive polishing pads but the simple piece of cloth

will work very well.

Slide Mounting.

There are a number of different micro-slides available (medical,

petrographic etc.) plus you can make your own like the ones I make tofit a 35mm slide projector. It does not matter what you use but be

sure to cut your specimens to fit the format of the slide before

grinding.

All slides must be cleaned thoroughly. This is a most important step inmaking a successful slide. No slides are clean as delivered by the

factory, in fact, they can't be. If the glass slides were perfectlyclean cohesion of the glass surfaces would make it impossible for you

to pry them apart. To avoid this manufacturers use a light dusting of

powders like talc or thin films of silicone oils on the glass to keepthem from sticking. This must be completely cleaned off for bonding to

be strong enough to resist the tremendous shearing forces ofpolishing. The best method of cleaning is to use Tri-Sodium Phosphate

(TSP) as a water soluble cleaner followed by denatured alcohol. I havesuccessfully used Windex as the water soluble cleaner and 95% Isopropyl

alcohol. You should check each slide for any smears or films in

reflected light and take every effort to get the slides scrupulouslyclean.

Lay the slides on a layer of paper several sheets thick on a solidflat surface. Be sure the surfaces are clean. For bonding agentsepoxy or any of the cyano-acrylic glues such as Super-Glue or PaleoBond

can be used. I prefer the latter as they are a bit more brittle andthus grind better but they frequently require the application of a

cover glass after polishing. Epoxies tend to be tougher but more

plastic, which slows the grinding (actually the rock will grind muchfaster than the glue) and slows the polishing, plus the glue itself

rarely polishes to clear. If you do use epoxy you should avoid thefastest setting glues (5 min) and go for the longer (20 min. or longer)

as these have different chemical formulae and bond to the glassbetter.

With the cyano-acrylic glues you should individualy put a drop or two(depending on the size of the piece) on the glass slide and take the

specimen and push it into the drops, centering it on the slide andworking it back and forth a bit so excess glue and bubbles are forced

out the sides. If there is any dirt between specimen and glass it canbreak either of these or will form a wedge between them that will

later ruin the slide. Unlike many other uses the glue will not bond

with it's usual quickness here. You have a minute or so to arrange thespecimen. You may want to use popsicle stick or some such soft prod to

push the specimen around as the glue will bond the slide or specimen toyour fingers much faster than the specimen to the slide. It will take

at least 24 and maybe 48 hours to get this glue to completely harden.After 24 hours it is advisable to go back and put a bead of the glue

around the edge of the specimen to seal it in well. It also helps ifthe slide can be very mildly warmed. A screen over a lamp shade with

slides resting on it in the warm flow of air works very well. They


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should not get hot, only warm.

If epoxy is used mix enough to do four or five slides at a time. Donot try to do too many at once. For your first attempt just do one or

two. Take a popsicle stick and wipe the glue on the specimen first to

fill any pores. Then put a drop or two on the slide and push the sampleinto it working it back and forth a bit to seat it and get a good bead

of glue around the outside. Do not use too much glue. It will become amessy job and a wide glue margin around the work will slow grinding and

polishing. These will need 24 hours to bond completely before anygrinding.

In both cases, after the glue has set but not bonded you can look at

the backside to inspect for bubbles. It is unlikely that there will beany but wherever there are will be a weak spot in the slide that may

cause problems later. There is virtually nothing that can be done tofix this so you will have to be aware of it as we go on and treat this

slide with greater care.

Thinning.

Now that the little rock slab is glued to the glass microscope slide onit's polished side it is necessary to grind it down to the required

thickness for transparency so you can literally see through rock

without x-ray vision, even if the rock were kryptonite! The mostimportant thing now is to make sure the front surface being ground

becomes parallel to the glued down polished side, or the surface ofthe microscope slide itself. The latter is much easier. For this task

you will need some sort of shim stock. This is just thin metal that canbe cut with scissors. It is desirable to have several thicknesses.

Aluminum flashing will work though it is a bit soft. Better is brass

shim stock available at hobby shops and hardware stores. Cut severalstrips from the thickest stock about 1/4" to 3/8" wide and the full

length of at two times the width of the slide. Take one of thethickest strips and a blank microscope slide and wrap the piece of shim

stock around the short dimension of the slide (see diagram at end ofpaper). This will be called the "clip" and two of these will be

needed. One side of the clip will span the slide and the other will

probably not or will overlap. Put the clips on the working slide so theside that spans the slide is on the rock or working side of the slide.

There should be a clip on either side of the specimen. The object will

be to grind the rock specimen down to the level of the clips. If youwrapped them carefully around the blank slide such that there is nobubble, bow or kinks in the clip surface, then when the specimen is

ground down it will the same thickness across and parallel to the frontsurface of the slide.

A technique that has worked well is to grind the specimen down with 220grit to the level of the first clip. This will be something less than

1mm thickness. Then wash up and go the next thickness clips and thenext grit. By this time the specimen should be getting translucent

when held up to a light and fossils should be visible though notclearly. With the second to the last grit (depending on how many

grades you want to use, in my case the 5 micron grade) grind the slide

down to almost the desired finished thickness. The last grade ofabrasive will be used with no clips and should be used only to remove

the pits from the previous grade and any final touch-up on thethickness or "wedge".

"Wedge" is when one side of the specimen is thicker than the other. As

you hold it up to the light one corner or side will be darker than the

other. The cause can be poor grinding, a defective clip, a bit of gritor dust under one end of the specimen when it was glued down or a

combination of these. It can be corrected. When grinding in these finalstages put the finger tip pressure over the darkest area. The slide and

specimen are fairly flexible now and this will put a little morepressure on that spot causing it to grind a little more in that spot.

Go slow with the grinding in these stages, don't rush. You've put a lot

of work into this and you don't want to wreck it now. Inspect the work


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frequently. When you can clearly see details in the fossils through thesample, go to the last grinding grit. If a fossil pops out of the

sample or disintegrates in grinding, as can most often happen withfusilinids, or the specimen grinds through above a trapped bubble in

the glue underneath, then stop and go to the final grind stage. If you

are in the final grind when this happens then go straight to polish.This will not produce a high quality slide but it will save the slide

to that point. To go on further with the grind would result in thedisintegration of all or most of the slide. Better to have something

than nothing!

Use the last grinding grit until the work has a shine to it when a

light is reflected off of it at a low angle. Try to remove wedge butin a first effort this may not be successful. This is not a disaster.

The last wet with the finest grinding grade should be with very lightpressure and should just skid about on the glass tool. This will

smooth out the pits of this final grade and make the polish go eveneasier.

Final Polish.

Once you have a good grind where you can see a reflection of a light

bulb off the work when viewed at a glancing angle (see diagram at endof paper), and the specimen is quite transparent, then it is time to

polish. Again, the piece of denim or twill is wrapped around the wellcleaned grinding tool and a charge of cerium is applied to the cloth.

Polish until the adhesive is as clear as possible. The details in the

fossils will become more and more clear as the specimen takes on apolish.

Occasionally the glue will begin to peel at this stage, especially the

cyano-acrylic glues like PaleoBond. If this happens trim away some ofthe excess that is peeling with a razor blade or very sharp knife but

don't overdo it. Leave the best margin around the specimen that you

can. This peeling is a warning that the glue-glass bond is not as goodas it could be. It will be necessary to put a cover glass over the

specimen after the polishing.

Cover glass.

If it is necessary to put a cover glass on then wash the specimen and

slide well making sure all the polishing residue is gone. Then let it

dry for a day. Obtain a set of microscope cover glasses or cover-slipsfrom a hobby/science shop or from a scientific supply house. Also tryand get a low viscosity cyano-acrylic glue and its solvent. The latter

is most important. The larger cover glasses are best to ensure theentire sample is covered. I use some that are nearly 1x1.5 inches. If

you are using the smaller ones (1x1cm) then one drop of a thin

cyano-acrylic glue is all that will be needed. In fact, it willprobably be too much. Apply the drop and gently push the cover into it

softly applying pressure. Watch out that the glue does not get on thefingers. Wipe the excess with tissue or paper towel and don't worry

about smears at this stage. You will have about 30 seconds to placethe cover glass correctly so waste no time. Your first effort may not

be a work of art. We can fix some of that, but a crooked cover glass is

permanent.

After a few minutes, when the cover glass is well affixed, get a tissueand put several drops of the solvent on it. Use this to clean up the

excess glue and smears. You'll be pleasantly surprised how readilythese clean up. Stubborn drops and glops of glue can be coaxed free

with a single-edged razor blade.

Other things that can be thin sectioned.

There is virtually no limit to the things you can section and enjoy. Myown introduction to this was when the Arizona-Sonora Desert Museum

(ASDM) asked me to look for fossils in the matrix from the Sonorasaurussite south of Tucson. As luck would have it, there was not a fossil to

be found in the matrix with the possible exception of a tiny,


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fragmentary coprolite. The soil was very quartzitic and well sortedindicating a probable swift flowing stream deposition. But there were

Sonorasaurus bone chips in the matrix and these did fascinate me. Ithen and there decided to make my first thin sections, and the only

ones to date of the Sonorasaurus. When I saw the internal bone

structure I was amazed. I had no idea such structure existed. Next, Idid library research on bone histology and particularly books and

papers on dinosaurian bone histology at the Univ. of Arizona Libraryand spent the summer of 1996 pouring over them and making thin

sections of all the dino-bone I could lay my hands on. I had an ideathat perhaps by measuring the diameters of the cellular structures in

the dense bone, called Haversian Systems, I could make comparisons with

other dinosaurs. My results are summarized in the paper given at theFossil in Arizona conference for that year and co-authored by Ron

Ratkevich formerly with the ASDM. Statistically, the secondary osteondiameters most resembled hadrosaurians and sauropods and not

ceratopsians or carnosauria. (Reic, R.E.H. 1966)

I then embarked on a thin section exploration of many fossils and

fossiliferous rocks. I have made sections of bones from the Devonianthrough the Pliocene and teeth as well. This technique lends itself

well to making good use of bone chips and fragments, particularly ifthe parent creature is known. My wife, a meteoriticist with Lunar &

Planetary Lab at Univ. of Arizona, has pressed my talents into serviceon igneous rocks as well, but they're not nearly as interesting now are

they?

So the only limit to what you can section is your imagination. It is a

powerful tool in determining ages, populations and doing statistics onall sorts of fossil facies.

How to stabilize crumbly matrix or bones.

One problem that does come up with some materials is stability of the

fossils and/or matrix. This can be dealt with by several methods. Forthe most porous materials, soak the little sample with cyano-acrylic

solvent and immediately put glue on it so as the solvent evaporates itpulls the glue into the specimen. Let this dry for a day or so and

then put more of the glue on the outside. It should be hard enough bythen to allow you to proceed with the processing.

If a specimen, particularly hard brittle bone, crumbles from theperimeter as you grind, it may be best to coat it with epoxy or even

encase it in a block of the material. This is frequently the case when

working teeth. Broken and chipped teeth are cheap and very identifiableas to the original owner, usually right down to the species. This makesthem very desirable as specimens. But they are also crumbly because of

the strong layering. So it is usually necessary to encase them inepoxy just to keep them in one piece even after soaking them as above.

One word of warning from the opposite side of this problem. Some thingsare incredibly hard and resistant to grinding. Notably among these are

dinosaur egg shells. The shell of the Titanosaur from Argentina is thehardest thing I have ever had to grind and just to get it down to a

millimeter it was necessary to use a grinding wheel! The smell isstrong and oily, worse than any Green River shale.

Fixing broken slides.

It will happen that you will break a slide. As Murphy would have it,

this will be one of your better works. All is not lost as long as thebreak does not occur through the specimen, but the remedy is tricky.

Take another microscope slide the same size as the broken one and using

the mounting glue (either type) glue the broken one to the new slidealigning it as best you can. Epoxy may be preferable for this job since

it will not set up as fast as the cyano-acrylic glue but it is moreprone to bubbles on such a large surface. Put a large drop or two in

the middle of the slide and push the other squarely into the work.Work the two slides against eachother well to force out any bubbles and

don't use too much glue or the job will get quite messy.


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Labeling.

This is done by running the slide up and down along the straight sidewith the portion to be frosted grinding on the surface of the tool.

Finding a permanent but still small enough font label was difficult and

is still an ongoing process. The best solution so far has been the oldtried and true method of hand lettering with pen, nib and india ink on

a frosted end of the slide. We know this will work and last for atleast a century. If your slides do not already have a frosted or fine

ground end on them it will be necessary to make one. This is simplydone by using a flat piece of glass with one straight side. , some 400

or 600 abrasive and grinding the section you want (see diagram at end

of paper).

Keep good records. This is very important should you find something newand unusual. Unlike with megafossils as there is an additional stage of

separation from the original source. With an ordinary megafossil thespecimen is collected in the field catalogued, stored and labelled.

With microfossils, particularly with thin sections, the specimen is

collected, cut out of the original matrix, prepared, then catalogued,stored and labelled. So it is very important that it be traceable back

to the point of origin as specifically as possible. This does not meanthat an unidentified fossiliferous rock cannot be useful. Thin sections

from such a rock can be educational and just plain fun to look at.Frequently, when at a show, a particularly interesting fossil laden

rock will catch our eye. It will be poorly labelled or unlabelled butis reminiscent of several possible formations. A thin section, followed

by analysis of the biota therein can, in many cases, nail the point of

origin!

Microscopes

You do not need a fancy Bausch & Lomb binocular microscope with cameraattachments and special illuminators to enjoy your slides. There are

a number of much more economical means to view your work. Radio Shack

and some hobby shops have very economical hand held microscopes atreasonable prices. These are alright for a single viewer but what about

a bunch of people. As I said before, I make some of my slides in 35mmslide size. The specimen is usually made to fit the opening in a 35mm

slide mount so when I am finished I can glue a 35mm slide frame to oneside of the glass, to prevent breakage and to block light around the

specimen. Then I only need to project the prepared slide like any

other photographic slide and I have a microscope with which I can studymy slide in comfort without having to squint through an eyepiece.

Another relatively inexpensive, low powered microscope is the oldmicrofiche reader. These can be had at junk stores, garage sales andgoing-out-of-business sales for very little money. The slide, in fact

up to half a dozen, can be put in the carrier at one time and studiedby many people or yourself in relaxed comfort again not having to

squint through the eyepiece.

What to do with these?

Now you may proudly examine your handiwork. There may be a couplebubbles in it and it may be a bit thicker on one end than the other,

but still it will show you a whole new world of fossil flora and fauna

that will fascinate you for hours. Try making sketches of the thingsyou see and then identify them. A lot will be learned from this

process. Build a library of papers and books on the formations you wishto study. Identify the fossils in your sections. It is a good idea to

get a book on paleontological thin sections. These have been publishedby oil companies, societies and associations of economic geologists and

paleontologists and are not too costly on the used market. (Johnson)

Learn to make sketches of these fossils and keep a book of them. Manywill not be identifiable at first. Keep at it. It may take years to

make positive identifications of all the fossils on a given slideduring which time you will have undoubtedly made more slides that will

also have unidentified creatures on them. Eventually you may evendiscover a new one. This is very possible in the world of microfossils

and thin sections.


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References:

Allman, Michael, and Lawrence, David F., (1972) Geological Laboratory Techniques, ARCO Pub. Co., Inc,

York.

Johnson, J.H., (no year) Recognition of Organic Debirs in Thin Sections of Limestone, Tenneco Oil Co.

Jones, Daniel J., (1956) Introduction to Microfossils, Harper & Brothers, p.7-18.

Kummel, B., and Raup, D., (1965) Handbook of Paleontological Techniques, W.H.Freeman and Co., San

Francisco.

Reid, R.E.H., (1996) "Bone Histology of the Cleveland-Lloyd Dinosaurs and of Dinosaurs in General, PartIntroduction: Introduction to Bone Tissues", Brigham Young Univ. Geological Studies, Vol.41.

making thin sections by hand

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