320 



CONCLUDING EEMAEKS ON 



[Ch. XIV. 



whereas, 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 thick- 

 ness to any amount. It may also extend horizontally over a 

 broad area, as the water gradually encroaches on the subsid- 

 ing 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 constant upheaval, 

 will usually be too slight in thickness to endure for ages. 



In proportion as we become acquainted with larger geo- 

 graphical areas, many of the gaps, by which a chronological 

 table, like that given at page 139, is rendered defective, 

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

 of Prof. Sedgwick and Sir Roderick Murchison, to inter- 

 calate, in 1838, the marine strata of the Devonian period, 

 with their fossil shells, corals and fish, between the Silurian 

 and Carboniferous rocks. Previously the marine fauna of 

 these last-mentioned formations wanted the connecting links 

 which now render the passage from the one to the other 

 much less abrupt, 

 tween the Permian and Liassic strata, is filled up on the con- 



* 



tinent by the marine Trias of Germany where the Muschel- 

 kalk, as well as the St. Cassian beds occur, both of them 



* 



rich in marine fossils. The Upper Miocene has no represen- 

 tative in England, but in Prance, Germany, and Switzerland, 

 it constitutes a most instructive 

 creation and the middle of the great Tertiary period. Still we 

 must expect, for reasons before stated, that chasms will for 

 ever continue to occur, in some parts of our sedimentary 

 series. 



Concluding remarks on the consistency of the theory 



So the hiatus subsisting in England be- 



link between the living 



gradual change, with the existence of 



breaks in the 



series. — To return to the general argument pursued in this 



chapter, it is assumed 



reasons above exjjlained, that a 



slow change of species is in simultaneous operation every- 



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