740 



REroiiT — 1884. 



Mm 



m 



il i:i' 



many countries, it would be rash in tlio oxtremeto infer the synchronism of portions 

 of these when separated by deirrees of hititude. The time required for these zones 

 to travel from Kent to the Crimea, and to accumulate a mass, mainly coniposefl 

 of minute organisms, of over a thousand feet in thickness, must have been sutlicient 

 to account for a very sensible pro<:ress in the evolution of organic forms. 



The de])osition of the (.!halk commenced in the I"]nglish area at a period when 

 the land lloras were still of Jurassic character. J>y Ihe time it had reached 

 Limburg, Saxony, and Boliemia, Dicotyledons had become developed. The pcrioil 

 required for the chalk ocean to encroach but JiOO to 400 miles must thus liavi' been 

 very vast. The question may however arise, whether plant development at rliis 

 stage followed the otherwise universal law of evolution, or was excejitionally rapid. 

 The fauna has to b(; examined to see wliether it discloses an equally appreciiil/1" 

 progress. The conclusion arri\ed at is, that while the groups with which the 

 author is less acquainted apparently do so, the progress in the Mollusca is imniis- 

 takabh^ The helicoid, turbinate, and patelloid groups are archaic and stationary, but 

 the fusilorm shells betray a tendency to elongate their canals, and the relative 

 abundance of such, and gradual dropping out of now extinct genera, furnish an 

 unmistakable index of the relative ages of the more littoral deprsits. From this 

 point of view we are able to demonstrate that the Greensands of Aix-la-Chapelh' 

 are far younger than their lithological structure and sequence would indicate, 

 while the appearance of such distincily new developments as cone and cowry sliells 

 further support the views of tli ■ ndatively almost tertiary, or, at least, transition 

 age of the Cretaceous series iu Denmark. While, therefore, denudation on a truly 

 colossal scale iias produced one of the most considerable gaps in the whole 

 geological record between Cretaceous and Tertiary over the British area, beds of 

 intermediate age may successfully l)e sought for at a distance from this centre. 

 The erroneous correlation of these, bed by bed almost, with the typical Cretaceou,- 

 series, as developed in England, has led to a still more untrustworthy correlation of 

 the American series with ours. 



The Cretaceous series of America contains at its very base a flora composed of 

 angiosperms so perfectly differentiated that they are apparently referable to 8x181111!,' 

 genera. One of the oldest floras in Europe containing angiosperms is that of 

 Aix-la-Chapelle, and even this we have seen is relatively modern : but these are 

 not referable iu at all an equal liegree to existing genera, and even the (^oniferae 

 are embarrassing on account of their highly transitional characters. The oldest 

 Cretaceous flora of America, so far from possessing any Cretaceous characters, 

 agrees iu a remarkable manner with that of the F " ^ Lower Eocene, wliile the 

 Laramie, or supposed Cretaceo-Eocene, flora has veij much in common with tliat 

 of our Middle Eocene, and marks a similarly sudden rise iu temperature. The 

 question is whether the evidence of the fauna in favour of the Cretaceous age 

 of the series is so conclusive that the floral evidence must be set aside. Tallin;,' 

 the Cretaceous series as represented in California, the older stages possess ^lollusca of 

 definitely Cretaceous aspect, but those of the newest have a decidedly Eocene facies. 

 To be Cretaceous a fauna must have some elements which did not survive to a later 

 period ; but are we in a position to state that the Ammonitidfc, the Belemnites, 

 and Inocerami did not do so ? Even our present limited knowledge is entirely 

 opposed to such a view. It must be remembered that the Eocenes in their typical 

 area, England and France, were deposited under peculiar local conditions, and it 

 would be as logical to infer from the absence in them of Cretaceous types that 

 these existed nowhere else, as it would be, were the bed of the English Channel 

 now upheaved, to class as extinct all forms of life not met with in its sands and 

 muds. If, as there is evidence to show, America was isolated at the time, the 

 survival there of forms of Reptilia, elsewhere extinct, would be iu accordance with 

 ordinary observation at the present day. 



The flora of the American series is Eocene ; the fauna of its earlier stages h 

 Cretaceous. We are compelled, therefore, to choose whether we will believe that 

 a large Eocene flora was developed there during the Cretaceous, or that some 

 members of a Cretaceous fauna lived on to an Eocene date. The former supposition 

 demands greater rapidity of evolution than we are accustomed to admit, and uo 



