130 BRITISH EOCENE FLORA. 



The Break Between the Cretaceous and Eocene Rocks in the 



British Area. 



It is a remarkable fact that the extermination of so much that was pre-existing of both 

 the marine and terrestrial Fauna, embracing nearly all the shelled Cephalopods and all the 

 gigantic Saurians which had till then occupied the foremost place, should have been accom- 

 panied by a similar wholesale disappearance among Plants. To suppose that this period 

 was an exceptionally fatal one, annihilating entire orders of the animal kingdom, is to admit, 

 in the complete absence of evidence, a break or jerk in the majestic progress of life upon 

 the earth ; and this is repugnant to common sense. It is more consonant with our 

 present views to suppose that we are in presence of one of those vast gaps in the geological 

 record which we know must have occurred over and over again in every upheaved area 

 upon which sedimentary rocks had been deposited. In turning from the last Cretaceous 

 deposit in Europe, we seem, so far as the Plant world is concerned, to finally break with the 

 past, while the first deposit of the Eocene appears like turning over the first page of the 

 history of things as we see them now. It is thus, perhaps, worth while to turn aside 

 for a moment to take stock, as it were, of the closing events of the Cretaceous, so far as 

 we know them at present, in order to estimate the true nature of the apparently sudden 

 bound in the usually stately and measured march of evolution. 



It appears that during the Chalk formation a great wave of depression passed across 

 Europe, travelling from the west to the east, permitting the ingress of the Atlantic, and 

 forming a gulf over what is now Central Europe, which constantly increased in magnitude. 

 We need not believe that this gulf was formed by any sudden catastrophe, for there is no 

 reason to doubt that the sea conquered the land by the same methods and at somewhere 

 about the same rate that it encroaches now, and that therefore its advance over many 

 thousands of square miles of terra firma would be an exceedingly lengthened process. 

 We cannot gauge the time this occupied ; but we know that since the appearance of Man 

 Southampton Water has been formed, and a tract between Alum Bay and Studland, 

 some fifteen miles long and five or six miles broad, has been swept into the sea, and 

 several species, like the Mammoth, have become extinct. The rate of the encroachment 

 depends mainly on that of the subsidence and the original height of the land, but what has 

 here been effected in a subsiding area serves to show roughly how vast a time must have 

 been needed for the chalk sea to have crept from Kent to the Crimea, and to have covered 

 the enormous area of Europe over which its traces still remain. As the land subsided and 

 became sea, blue and green muds were thrown down, to be succeeded in due course by the 

 deeper deposits of chalky ooze. It would be physically impossible for the Chalk, supposing 



