92 ON THE PHrSICAL HISTOEY OP THE CEETACEOFS ELINT8. 



It would be interesting to compare analyses of Chalk where there 

 were many and where there were no layers of flint. He mentioned 

 a case where one of the green-coated flints at the base of the Thanet 

 sand was imbedded in a band of white flint in the Chalk below, 

 which latter, therefore, must have been formed round the former. 



Mr. HuDLESTON said that Mr. Mortimer, in a recent paper, had 

 stated that the upper flintless Marsupite Chalk of Yorkshire con- 

 tained twice as much silica as the middle or flint-bearing Chalk. At 

 North Grimston, in the Coral Bag, where the beds were flat, there 

 was no flint ; where they were bent, there were many flints. 



Dr. Wallich said Mr. Charlesworth had quite misunderstood him 

 about Dr. Bowerbank's and Mantell's views. The time at his 

 disposal forbade his going into the whole question ; but, briefly, his 

 view was that the sponges attracted the colloidal silica which existed 

 at the surface of the mud. 



