14 PRINCIPLES OF GEOLOGY, 



cline at great angles into the earth, and in several instances are placed 

 directly vertical. The planes of strata are usually continuous and unin- 

 terrupted over large spaces, but occasionally they are broken by faults, 

 and divided by dykes. It has been a question whether these unusual 

 positions have existed from the first accumulation of the rocks, or been 

 caused by subsequent convulsions. 



It is agreed among geologists that many of the primary, but at least 

 all the secondary rocks were deposited by subsidence from water. Matter, 

 so deposited, in some degree accommodates itself to the surface on 

 which it drops ; but it must especially tend to form horizontal layers : 

 and it is well known that strata have generally only a moderate incli- 

 nation. If the bottom be level, so will be the deposit ; if gently sloping, 

 the deposit will be inclined ; but if there be a perpendicular subaqueous 

 cuff, no sediment can fall upon it. A perpendicular layer arising from 

 sediment is impossible. Whenever, therefore, we behold vertical strata 

 which contain evidence of deposition, we may be quite sure that they 

 were not deposited in that form, but have been displaced by some violent 

 internal motions in the earth. There are some remarkable instances of 

 contorted stratification, which require the same explanation. It is absurd 

 to maintain that such flexures are original, assuredly they have been 

 occasioned by operations subsequent to the accumulation of the rocks in 

 question. But the most remarkable case of unusual position is when 

 strata, either horizontal or inclined, are broken, and their planes inter- 

 rupted, so that on one side of the line of fracture the rocks are higher 

 than on the other : this difference of level sometimes amounts to one 

 hundred or even two hundred yards. (For examples, consult the section 

 of the coast at Red cliff, Scarbrough castle, and the Peak, near Robin 

 Hood's Bay.) The succession of strata is, on each side, the same, and 

 it seems hardly possible to doubt that they were once connected in con- 

 tinuous planes, and have been at a subsequent period forcibly broken 

 and disjoined. This opinion is, and deserves to be, universal. The line 

 of separation between the elevated and depressed portions of strata is 

 generally nearly vertical, and distinguished by a fissure, which in faults 



