SIR CHARLES LYELL 219 



connection with those of a second period found in India, and will 

 therefore no more enable us to trace the signs of a gradual change 

 in the living creation, than a fragment of Chinese history will fill up 

 a blank in the political annals of Europe. 



The absence of any deposits of importance containing recent shells 

 in Chili, or anywhere on the western shore of South America, 

 naturally led Mr. Darwin to the conclusion that "where the bed of 

 the sea is either stationary or rising, circumstances are far less favour- 

 able than where the level is sinking to the accumulation of conchif- 

 erous strata of sufficient thickness and extension to resist the average 

 vast amount of denudation." In like manner the beds of superficial 

 sand, clay, and gravel, with recent shells, on the coasts of Norway 

 and Sweden, where the land has risen in Post-tertiary times, are so 

 thin and scanty as to incline us to admit a similar proposition. We 

 may in fact assume that in all cases where the bottom of the sea 

 has been undergoing continuous elevation, the total thickness of sedi- 

 mentary matter accumulating at depths suited to the habitation of 

 most of the species of shells can never be great, nor can the deposits 

 be thickly covered with superincumbent matter, so as to be consoli- 

 dated by pressure. When they are upheaved, therefore, the waves 

 on the beach will bear down and disperse the loose materials ; where- 

 as, if the bed of the sea subsides slowly, a mass of strata containing 

 abundance of such species as live at moderate depths, may be formed 

 and may increase in thickness to any amount. It may also extend 

 horizontally over a broad area, as the water gradually encroaches on 

 the subsiding land. 



Hence it will follow that great violations of continuity in the 

 chronological series of fossiliferous rocks will always exist, and the 

 imperfection of the record, though lessened, will never be removed by 

 future discoveries. For not only will no deposits originate on the dry 

 land, but those formed in the sea near land, which is undergoing con- 

 stant upheaval, will usually be too slight in thickness to endure for 

 ages. 



In proportion as we become acquainted with larger geographical 

 areas, many of the gaps, by which a chronological table is rendered 

 defective, will be removed. We were enabled by aid of the labours 

 of Prof. Sedgwick and Sir Roderick Murchison, to intercalate, in 

 1838, the marine strata of the Devonian period, with their fossil 



