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The Yorkshire chalk is not so well suited for microscopic 

 examination as that of the South of England, nor are the 

 flints which abound in it so rich in organization as those of 

 Kent and Wiltshire. They appear, however, to contain, 

 though in less abundance, the same minute organizations. 

 Flint, with a peculiar cloudy, mottled, textural arrange- 

 ment, which Mr. Bowerbank refers to sponge, contains 

 imbedded in its substance several kinds of minute struc- 

 tures, of which the so-called Xanthidia are the most 

 remarkable. In general, I find in the chalk and flint a 

 quantity of organization, continually increasing in propor- 

 tion to the clearness and perfection of the microscope. 

 Not a small part of the mere powder-grains are single 

 cells of the Rotalia and Textilaria. (See Fig, 7 for the 

 outline of a Rotalia.)* 



Among the numerous lacustrine deposits on the coast of 

 Yorkshire, of which 16 years ago I published the descrip- 

 tions, one has often since attracted my attention, from the 

 great probability of its containing Infusorial animalcula. I 

 allude to the peculiar white and brown cretaceous marly 

 deposits, a quarter of a mile north of Bridlington. I 

 have often examined this marly substance, but my instru- 

 mental means, till within a few years, were inadequate to 

 the research. The Rev. W. V. Harcourt found it to contain 

 a certain proportion of silica. I have repeated this experi- 

 ment, and find among the siliceous grains left by the 

 action of dilute acid, a considerable number of Loricated 

 Infusoria, chiefly of the genera Navicula, Cocconema, Bacil- 

 laria, and Eunotia. I have also been fortunate enough to 

 discover a new species of the rare genus Campilodiscus 

 in this marl ; and as occurrences of this kind are not 

 frequent in England, and as no fossil Infusoria have been 



* Dr. Mantell has found in the substance of flint not only the shells but the 

 animal substance of Rotalise. 



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