Composition f and Analogies of Rocks, 211 



why the angles of the fragments are so little rounded, and why 

 the separated parts are so capable of being re-adapted. It is 

 easy to conceive also, that the infiltration of a solution of lime 

 would convert them into a solid rock, and that the same effecta 

 might, under other circumstances, take place from carbonate or 

 rust of iron, or from some other of the causes that produce the 

 consolidation of rocks. 



The several conditions thus hypothetically stated, appear to 

 have frequently existed in nature, and thus have arisen the num- 

 ber of local conglomerates now seen. 



The fractures of the rock, and the consequent production of 

 fragments on the surface, have probably, in all such cases, ori- 

 ginated jointly from the ordinary causes of waste and from me- 

 chanical violence. In some instances, where the conglomerates 

 lie between two rocks, they seem to have resulted from the 

 motion of the parts on each other, in consequence of sudden and 

 violent fractures, accompanied by a partial comminution of the 

 materials. 



Where one rock alone has been engaged, a conglomerate of one 

 ingredient, united by a general cement, is the result ; and this 

 case is frequent in the calcareous rocks. When the fractures have 

 taken place at the meeting of two strata of different rocks, or 

 when two have been in any other mode implicated, the compound 

 is more intricate. Thus also there are formed conglomerates of 

 limestone and serpentine, or of limestone and argillaceous schist, 

 or of other substances. 



There is little now to be said respecting the formation of the 

 unstratified rocks, which does not follow from the views of their 

 origin now generally received. Of their materials, we can only 

 know that they are those which are also found in the stratified 

 substances, and can only conjecture, indiscriminately, that they 

 have been formed by the fusion of some or other of these. Dif- 

 ferences in the proportions of the several earths are the only 

 grounds of judgment ; and thus it would be inferred that granite 

 was the produce of gneiss, micaceous schist, quartz rock, and ulti- 

 mately of argillaceous sandstones, and that the ordinary traps 



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