04 



LYELL'S ELEMENTS OF GEOLOGY. 



Rising and Sinking of Land Vertical, Inclined, and Curved Stratification. 



It has also been shown by Mr. Darwin, that, in those seas 

 where circular coral islands abound, there is a slow and con- 

 tinued sinking of the submarine mountains on which these masses 

 of coral are based ; while in other areas of the South Sea, where 

 coral is found above the sea level, arid in inland situations, and 

 where there are no circular or barrier reefs, the land is on the 

 rise.* 



It would require a volume to explain to the reader the various 

 facts and phenomena which confirm the reality of these move- 

 ments of land, whether of elevation or depression, whether ac- 

 companied by earthquakes or accomplished slowly and without 

 local disturbance. Having treated fully of these subjects, in the 

 Principles of Geology, I must assume, in the present work, that 

 such changes are part of the actual course of nature ; and when 

 admitted, they will be found to afford a key to the interpretation 

 of a variety of geological appearances, such as the elevation of 

 horizontal or disturbed marine strata, the superposition of fresh- 

 water to marine deposits, and many other phenomena, afterwards 

 to be described. It will also appear, in the second part of this 

 volume, how much light the doctrine of a continued subsidence 

 of land may throw on the manner in which a series of strata 

 formed in shallow water may have accumulated to a great thick- 

 ness. The excavation of valleys also, and other effects of denu- 

 dation, of which I shall presently treat, can alone be understood 

 when we duly appreciate the proofs now on record of the pro- 

 longed rising and sinking of land throughout wide areas. 



Inclined stratification. The most unequivocal evidence of a 

 change in the original position of strata is afforded by their stand- 

 ing up perpendicularly on their edges, which is by no means a 

 rare phenomenon, especially in mountainous countries. Thus 

 we find in Scotland, on the southern skirts of the Grampians, 

 beds of puddingstone alternating with thin layers of fine sand, 



all placed vertically to the horizon. 

 When Saussure first observed cer- 

 tain conglomerates in a similar po- 

 sition in the Swiss Alps, he re- 

 marked that the pebbles, being for 

 the most part of an oval shape, had 

 their longer axes parallel to the 

 planes of stratification, (See fig. 

 57.) From this he inferred that 

 such. strata must, at first, have been 



Fig. 57. 



Vertical conglomerate and sandstone. 



* Proceedings of Geol. Soc. No. 51. p. 552., and his Journal in Voyage of the 

 Beagle, vol. iii. p. 557. 



