Principles of Geology. 13 



are placed directly vertical. The planes of strata are usually con- 

 tinuous and uninterrupted over large spaces, but occasionally they 

 are broken hj faults, and divided by dykes. It has been a question 

 whether these unusual positions have existed from the first accumu- 

 lation of rocks, or been caused by subsequent convulsions. 



It is agreed among geologists that many of the primary, and 

 all the secondary rocks were deposited by subsidence from wa- 

 ter. Matter, so deposited, in some degree accomodates itself to the 

 surface on which it drops ; but it must especially tend to form hori- 

 zontal layers; and it is well known that strata have generally only a 

 moderate incHnation. If the bottom be level, so will be the deposit j 

 if gently sloping, the deposit will bo inclined ; but if there be a per- 

 pendicular subaqueous cliff, no sediment can fall upon it. A per- 

 pendicular layer arising from sediment is impossible. Whenever, 

 therefore, we behold vertical strata which contain evidence of depo- 

 sition, 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, ei- 

 ther horizontal or inclined, are broken, and their planes interrupted, 

 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 hun- 

 dred or even two hundred yards, as on the coast at Red cliff, Scar- 

 brough castle, and the Peak, near Robin Hood's Bay. The succes- 

 sion of strata is, on each side, the same, and it seems hardly possible to 

 doubt that they were once connected in continuous 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 is filled 

 with mixed fragments of stone ; in dykes, by basalt or other rocks ; 

 but in mineral veins, with sparry and metallic minerals. 



The convulsions within the earth which have thus changed the in- 

 clination, altered the position, and broken the continuity of rocks in 

 so remarkable a manner, happened, of course, since the deposition 

 and induration of all the strata which have been thus dislocated. 

 But such progress has been made in inductive geology, as to render 



