252 PICTURESQUE SKETCHES 



trary, find the most nearly allied species existing 

 under very different conditions, and forming part of 

 a group whose physiognomy is distinct ; while, on the 

 other hand, very different species, traceable to sources 

 altogether different, may, and often do, show the 

 greatest physiognomical resemblance. We shall con- 

 sider in the next chapter how the different portions 

 of the great secondary period are distributed, and to 

 what extent they are alike. 



Before concluding these general remarks on the 

 chalk, it is necessary that I should here notice, how- 

 ever briefly, the uppermost beds of this period in 

 Europe ; those, namely, that occur on the banks of 

 the Meuse near Maestricht. From various appear- 

 ances it may be concluded that this deposit took place 

 not far from the shore. There have been found there, 

 for instance, the most perfect fragments of the Mosa- 

 saurus, the bones of turtles, &c., together with vari- 

 ous remains of crustaceans and shells, which bespeak 

 shallows occasionally left dry by the tide. No re- 

 mains of birds have, indeed, yet been obtained from 

 this spot, nor is there any indication of the extent 

 or direction of the land ; while, from the smallness 

 of this deposit, and the absence of distinct land fos- 

 sils, it might almost be concluded that there existed 

 only a few scattered islets in these European lati- 

 tudes. This locality is chiefly interesting from the 

 negative fact, that no modification of the fauna is 

 introduced in it. There is little positive evidence to 

 be derived from the few fossils there presented ; and 

 when we consider the aspect of the most ancient 

 tertiary fauna, it will be seen to bear no marks of 

 any association with this, which appears to repre- 



