MECHANICAL THEORY.

5

Nevertheless, the paper of Professor Sedgwick investedIke subject of slaty cleavage with an interest not to beforgotten, and proved the stimulus to further inquiry.The structure of slate-rocks was more closely examined;Ike fossils which they contained were subjected to rigidSc rutiuy, and their shapes compared with those of the sames pecies taken from other rocks. Thus proceeding, the lateMr. Daniel Sharpe found that the fossils contained in slate-y°cks are distorted in shape, being uniformly flattened out111 the direction of the planes of cleavage. Here, then, wasa fact of capital importance,—the shells became the indi-cators of an action to which the mass containing them hadeeQ subjected; they demonstrated the operation of pres-su re acting at right angles to the planes of cleavage.

The more the subject was investigated, the more clearly^®re the evidences of pressure made out. Subsequent toSharpe, Mr. Sorby entered upon this field of inquiry,rth great skill and patience he prepared sections of slate^° c k, which he submitted to microscopic examination, andjJ ls observations showed that the evidences of pressure coulde plainly traced, even in his minute specimens. The sub-Dct has been since ably followed up by Professors Haughton,

Harkne:

tioned

ss > and others; but to the two gentlemen first men-, . We are, I think, indebted for the prime facts onrests the mechanical theory of slaty cleavage.*

„ le reservations just referred to showed the co-existenceand 9 ^ W ° Phenomena, but they did not prove that pressureand C ^ eava S e s fo°d to each other in the relation of causeWas e ^ eC ^‘ £< ^ an the pressure produce the cleavage?”soirirf 1 ^ ^ °P en question, and it was one which mere rea-g> unaided by experiment, was incompetent to answer.

by ]yj xjau° r ^ tt S < t rawu m 7 attention to an able and interesting papercleavage . rsten ’ s ‘ Archiv ’ for 1840; in which it is announced that

to the exDe ' ° n ^ l0Q °t the mass produced by pressure. The author refersrimen s of Mr. Hopkins as bearing upon the question.