older Deposits of the North of Germany and Belgium. 227 



lusca (about which we were most anxious, and of which we had procured a 

 tine series) were pronounced by Mr. Sowerby, the moment he saw tliem, to 

 form a group analogous to that of South Devon ; an opinion valuable at any 

 time, but especially so now, while he is employed in describing and figuring 

 the South Devon fossils. At the same time we submitted the Eifel corals to 

 Mr. Lonsdale, who with equal confidence pronounced them Devonian. By this 

 interpretation of the fossils we were therefore confirmed in the opinion we had 

 formed of the age of the systeme anthraxifere before we entered Belgium ; and the 

 sequence of the formations on the left bank of the Rhine disturbed not the classi- 

 fications we had first attempted to establish in the great series of older rocks on 

 the right bank. 



But for causes of inevitable delay, chiefly arising out of the long-continued ill 

 health of one of the authors, these results would have been laid before the Society 

 several months since. The recent investigations of Mr. Lonsdale, on the age 

 of the Belgian limestones, having meanwhile come before the public, we need 

 not refer to them in detail ; and have now only to express our thanks to him 

 for his most valuable assistance, and above all for the sanction he has given to 

 our classification by his careful analysis of some of the zoological evidences on 

 which it mainly depends. 



In closing this introduction we have now to state, that the memoir will be rendered 

 incomparably more effective than it could otherwise have been, by the valuable 

 cooperation of M. E. de Verneuil, who accompanied us during a part of our tour, 

 and generously determined, after having entered into our views, to render his 

 rich stores of organic remains (collected from the Rhenish provinces) available in 

 the illustration of this memoir. Undertaking the description of the fossil mol- 

 lusks of this region, he induced the Vicomte D'Archiac (eminent like himself 

 both in zoology and geology) to become his associate. These gentlemen have 

 drawn and described from their collections a series of the most characteristic of 

 the Rhenish fossil mollusca, particularly those of the Devonian and upper Silurian 

 groups ; and have furnished us not only with a scientific description of each 

 species, but also with a tabular arrangement of them, and with general theoretical 

 views, of high importance in determining the value of zoological evidence. In 

 justice to these authors, we trust that the force of their descriptions may not 

 have been weakened by translation. 



Lastly, the map which is annexed (and without which the description of the 

 Rhenish region and the sections would have been scarcely intelligible) is a re- 

 duction of the great map of Hoffmann, as improved by many recent observa- 

 tions of Professor Von Dechen and M. Erbreich, kindly communicated to us 

 by the former. This map, on which we have coloured the Palaeozoic rocks ac- 



