80 J. PATERSON ON DIAMOND FIELDS.

great carboniferous shales of the country, and as these seem toextend there not only over a wide area but also to a very greatdepth, the product to my mind of a great growth of weed, andreed, and grass, in the shallow waters of a widely extended lagoonwhich had once covered diamond land; imagination itself failsalmost to conceive the wealth of diamond production from suchbody or world of shales. Diamond-searching is no passing orfleeting enterprize there, but an abiding, continuing industry, notfor years only, but for ages.

2. ON OOLUMNAR BASALTS.

By JOHN OURRY, ESQ.

(Abstract.)

In the introduction the modern views by which heat is regardedas a vibratory motion were referred to. In accordance with theseviews cold must be considered as only a lower degree of heat, or alesser intensity of vibratory motion. Such being the only distinc­tion between heat and cold, it necessarily follows that a diminutionof the former is equivalent to an increase of the latter, and viceversa.

The process of the formation of columnar mud was brieflydescribed. The analogy between this process and that of theformation of columnar basalt being such that the, same diagramsserved for illustration in both cases, though in the former case heapenetrates the fine clayey sediments, and produces columns of driedmud; in the latter cold advances into the molten lava, and changesit into solid rock, which frequently has a rude, but sometimes aperfect columnar structure. In reference to the production of suchcolumnar structures the chief and most notable conditions are twodiverse temperatures, closely situated at the contact surfaces ofdissimilarly constituted bodies. The higher temperature theauthor designates heat, and the lower one cold. In the aboveinstances the dissimilar bodies in surface contact are, first, the at-

J. CURRY ON COLUMNAR BASALTS. 81

mosphere and the fine clayey sediments; second, the oceanicwater and the molten lava. While the solidifying of the lava isbeing effected, the solid and the molten parts may be considered asdistinct bodies. It is at and near the surfaces of contact wherethe exchanges of heat are most efficient in giving structure to theforming bodies. The actions of heat and of cold having directiveinfluence in the formation of hexagonal columns were shown in tbefigures of illustration.

During a long continuance of bot, dry weather, the cracking ofsoils and of fine clayey sedimentary muds into polygonal figuresmust be familial' to almost everyone. The lengths of the sides ofanyone of such figures are often variable. Figures having five,Fix, and seven sides are most prevalent. The hexagonal ones weretaken as the most perfect and suitable for illustrating the subject.A little after the commencement of desiccation the dried hexagonalmud figures are thin, and the openings bounding them are narrowand shallow: but as the heat advances downwards the formerthicken, and the latter grow wider and deeper. A long durationof extremely hot, dry weather increases the figures so in thicknessthat they ultimately acquire the columnar character. During theprocess of formation the heat progresses from the tops of thecolumns downwards, and carries the water from the centre of eachfigure, somewhat horizontally, into the lower parts of the openings,whence it rises to be expelled at the general surface. The waterthus carried off brings the particles of mud into closer union, and,consequently, angments their cohesive force. The laws of actionwhich regulate the formation of columnar mud are evidently verysimilar to those which produce the columnar form of wheatenstarch.

In dwelling on the formation of columnar basalts, it was sup­posed that much lava was erupted in the bed of the ocean, whereit found a resting place, under such conditions, so as to attainconsiderable depth and area, with its upper surface in a horizontalposition. In this case, the dissimilarly constituted bodies are theoceanic water and the lava; the former is the cold body, and thelatter the heated one. Thus, two diverse temperatures are closelysituated at the surfaces of contact. The extended level surface ofthe molten mass is exposed to the cooling influence of the oceanicwater. It is chiefly from this surface downward that the solidifica­tion of the molten mass must obviously proceed. When solidifica-

G

82 J . CURRY ON COLU MNA R BASALTS.

tion begins, hexagonal figures may be considered as forming, andas being surrounded by extremely small openings. A s the coldcontinues to proceed downwards, so do th ese figures of the solidify­ing lava augment in depth, and assume the columnar character.The openings bounding each figure are, doubtl ess, tb e result ofcontraction of the lava on, and afte r taking the solid sta te. Thediminution of heat, tbe expulsion of gaseous matter, and th e in­creased power of cohesion, may be referred to as causes of suchcontraction. The openings, which migh t in several insta nces bemerely divisional planes, would serve as channels for carrying offheat and gaseous matter upward into tbe ocean. Columns, formedunder such conditions as tbo se ju st described, would stand perp en­dicular ; but others occur which have a horizontal position. Toaccount for these, it was supposed, for example, that a deepnarrowish chasm is filled with lava, and that the sides of th e chasmmust be the chief cooling surfaces, consequently, tb e cold, advanc­ing from them towards th e interior, would solidify th e lava in th atdirection, and form horizontal columns. The auth or cited anexperiment by whicb drops of hot molten tallow , falling on th esurface of water, wbicb is near the freezing point, are quicklyarr anged into beautiful and often symmetrical figures, by th e law ofex.changes of heat, some of th em resembling flowers with sixpetals.

In tbe concluding part of the paper, the large surface contactsof tb e ocean with the bed on which it rests, and th e contact of theatmosphere with the land and water surfaces, were adverted to asareas where the exchange of heat bad done, and was now doingmuch work in producing structures. Jointage, cleavage, andvarious oth er rock st ructures, are ascribed as being mostly due tosuch work. The structure of ice is a mark ed example; it bears ast riking analogy to the hoxngonal columnar structure of basalts.I ce often breaks up into columns by slow meltin g. The ice of aluke sometimes shows such It breakage when it melts in thespring,