114 Proceedings. 



Upper Greeiisand, for geologists believe that it was accumu- 

 lated at a somewhat later date ; but this does not matter. 

 All that I want to show is that a slight upheaval of the sea- 

 bottom took place at the close of the Gault deposition. 

 Bat whatever small uprising of land may have happened then, 

 we have ample evidence that soon after— that is, soon, speak- 

 ing in a geological sense — a great and widespread depression 

 took place, for the ocean in which the Chalk was formed 

 was undoubtedly a deeper one than any we have yet con- 

 sidered. 



We are all of us pretty familiar with chalk. It is the most 

 striking formation of the south and east of England, and I 

 need hardly remind you of its connection with the name 

 "Albion." Its thickness at its greatest development is about 

 1000 feet. The most remarkable fact concerning it, and 

 which at the same time shows what an immense period must 

 have elapsed during its formation, is, that by far the larger 

 proportion of it is composed of the dead shells of the minute 

 Formninifera, so small that "hundreds of them would hardly 

 weigh a grain." It is separated into two divisions, the Upper 

 Chalk, with flints ; and the Lower, which occurs in our dis- 

 trict, without flints. This Lower Chalk has a large admixture 

 of clay, and much of it consists of the fragments of the 

 bivalve shell Inoceramus, which were secreted fi-om a very 

 brittle variety of carbonate of lime, the mineral Aragonite. 

 This brittleness is the reason why we so seldom find a good 

 specimen of the shell. 



Chalk is actually being formed at the present day in certain 

 parts of the Atlantic, at depths between 6000 and 14,000 feet, 

 where a substance is dredged up from the bottom formed 

 almost entirely of these Foram. shells, of the kind known as 

 Globigerina ; and as we do not find any great accumulation 

 of these shells in depths much less than 6000 feet, we infer 

 by analogy that the chalk ocean was of considerable depth 

 likewise. 



It was found during the voyage of the ' Challenger ' that on 

 this chalky bottom various animals flourished ; among them 

 Crustacea, Echini or Sea Urchins, and several Mollusca and 



