352 



Scientific Geology. 



were produced by some mechanical force, and not by igneous agen- 

 cy, I think is most manifest. And it seems to me that a power which 

 is adequate to the production of the cases which I have described, is 

 sufficient to account for a large proportion of the minor flexures and 

 contortions existing in clay slate, and mica slate; although I am not 

 aware that any examples similar to those which I have described, ex- 

 ist on the records of geology. 



So much for flexures and contortions previous to the consolidation 

 of the rocks. But these causes will not explain all the cases that oc- 

 cur. Sometimes we find alternating layers of quartz in the bent lam- 

 inae ; and it would seem that the rock must have been soft, when such 

 flexures took place. If we suppose the existence of a considerable 

 degree of plasticity in the layers, mere gravity (if the laminae were 

 in an inclined position,) would have produced flexures in them. In 

 other cases the force which elevated the strata might have operated 

 unequally and produced a similar result: though, as I shall attempt 

 to show hereafter, there is reason to believe that this force sometimes 

 acted laterally rather than from the interior of the earth. And some 

 flexures and contortions are explicable only by supposing such lateral 

 pressure. 



Some facts lead us to suppose that mere moisture operates power- 

 fully, deep in the earth, to render the strata flexible. Some limestones 

 and sandstones exhibit this flexibility ; and even granite in some deep 

 quarries, is easily impressible. Hence the requisite plasticity may 

 have resulted in many cases from water. But if the primary stratifi- 

 ed rocks have been partially fused, we have another source from which 

 this plastic state might have resulted. 



11. TALCOSE SLATE. 



I shall include in this formation the three rocks represented on the 

 map under the names of talcose slate, chlorite slate, and steatite. My 

 principal reason for adopting this arrangement, is, that in the works 

 of some of the ablest mineralogists, talc, chlorite, and steatite, are but 

 varieties of the same species : And when mineralogists are not agreed 

 that minerals are specifically distinct from one another, it seems to me 

 improper for geologists to regard those minerals as sufficiently charac- 

 teristic of different rocks, unless such rocks are widely diverse in their 

 relative situation and structure. But in the district under considera- 

 tion, it happens that the rocks mentioned above, are, for the most 



