J. LeConte—Fm-mation of the Coast Range of California. 303 



range at high angle. There can be no doubt, therefore, that 

 all the strata of this foot-hill region, including the slates, 

 underdip. the range at high angle. Evidently, therefore, the 

 cleavage planes of these slates " ' ' ' '" 



tion planes instead of cutting 

 as is most common. 



The diverse relation of the cleavage to the stratification 

 planes I explain as follows: In a thick mass of very fine sedi- 

 ments mashed together horizontally it is evident that the sur- 

 face and upper portions would first'' be thrown into one or more 

 close folds by which the strata are brought into a nearly per- 

 pendicular position, and then these would be thinned and 

 extended vertically by the pressure as already shown in the 

 previous portion of this paper : but the deeper portions would 

 be less and less folded, until, very deep, the folding would 

 cease altogether and the mashing would be by thickening only 

 and not by folding. I have rudely represented these facts in 

 the diagram, fig. 2, in which the parallel, nearly vertical lines, 

 represent the cleavage. In such a mass of horizontally squeezed 

 fine sediments, therefore, the cleav- 2. 



age of the upper parts would be par- 

 alhl with the strata while that of the \ 

 lower parts would be perpendicular 

 or nearly so to the strata. If, there- 

 fore, the upper parts only should be | 

 exposed by denudation" we would 1 

 have an example of cleavage parallel i 

 to the strata, and we might be in i 

 doubt whether to call the planes cleavage-planes or fine lam- 

 ination-planes ; but if greater denudation should expose the 

 deeper portions we would have an example of cleavage-planes 

 cutting throuoh the lamination-planes at a high angle and 

 therefore very distinct from them. 



3. It is evident from the above that in many cases the thick- 

 ness of the strata as we now find them may be very difler- 

 ent from that of the original sediments. In estimating the 

 latter, therefore, we must make due allowance for the great 

 thinning in some cases and thickening in others produced 

 hy pressure. 



4. In my paper on the formation of the great features of the 

 earth surface, already referred to, I have attributed mountam 

 elevation to horizont.-il crushing. Prof. Dana,* however, thmks 

 that, although the idea of plication is evidently included in my 

 ^■'ew, yet it ought to have a larger place than my words seem 

 to give it— ior the amount of elevation by plication is many 

 times ("ten-fold") greater than by simple crushing. 



* Am. Joum., in, V, 428. 



