IN THE MUD OF THE LEVANT. 11? 



tiary."* This conclusion appears to have been 

 arrived at by Ehrenberg in consequence of finding 

 certain orsranisms in them which occur in the Chalk; 

 but the evidence afforded by the higher forms of 

 Testacea and other animal remains, distinctly sepa- 

 rates them. Now, a close investigation of the 

 history of the Polythalamia, Diatomacese, and 

 siliceous Infusoria, so-called, will bring us to the 

 conclusion, that but little, if any, dependence can 

 be placed on them, as a means of identifying either 

 the age or the geological position of rocks. Be- 

 yond all doubt there exists in nature a number 

 of minute structures, cosmopolites, which appear 

 to be comparatively independent of the ordinary 

 influences of locality and climate. The fresh- 

 water pools of America, England, and Central 

 Europe, contain not only identical forms of Des- 

 midese, Diatomacese, and Spongillse, but there is 

 a closeness of resemblance in the aggregation 

 of their species which we do not usually observe 

 in the distribution of the higher forms of plants 

 or animals. Dr. Bailey has discovered few forms 

 in the United States that have not also been found 

 by Mr. Ralfs and his active coadjutors in England, 

 whilst most of the leading species observed by the 



* Phil. Mag. Vol. xviii. p. 38.i. 



