IN THE MUD OF THE LEVANT. Ill 



are wanting ; while, in the North of Europe, beds 

 of flint alternate with the Chalk, and marls with 

 Infusoria are wanting. This exchange of character 

 tends to explain the peculiar relation of flint to 

 Chalk, indicating that the pulverulent siliceous 

 particles of Infusoria have been converted into 

 compact nodules of Flint."* 



But there are reasons for believing that the 

 great facts upon which this hypothesis is based, 

 are incorrectly interpreted, and that no siliceous 

 Infusoria belonging to the Cretaceous era have 

 yet been discovered. The great siliceous deposits 

 of Virginia belong unquestionably to the Miocene 

 epoch. Those brought by Mr. Darwin from 

 Patagonia, form part of a recent Tertiary deposit, 

 and there is every probability that the Infusorial 

 layers of Sicily and Northern Africa will ulti- 

 mately be proved to belong to the Tertiary era. 

 I am not aware that any observer has succeeded 

 in verifying the alleged discovery of siliceous 

 Infusoria in the English Chalk, and the American 

 rocks which are unquestionably Cretaceous, have 

 as yet been equally unproductive. If these facts 

 be correct, of course the argument raised by 



* Phil. Mag. Vol. xviii. p. 385. 



