IV PREFACE. 



superposition ; beneath these the other formations are 

 sometimes so mixed, that it would be difficult to as- 

 sign them a regular mode of occurrence ; granite and 

 gneiss have however, according to the usual practice, 

 been placed at the bottom of the list ; the rocks usu- 

 ally termed trap rocks, have been thrown together 

 for the convenience of more easy reference. It is 

 not always very clear whether our lower chalk with- 

 out flints should be referred to the lower portion of 

 the upper white chalk of the French, or to their 

 craie iufau. I have inserted the rauschelkalk and 

 quadersandstein of Germany as separate formations, 

 in order to shew the opinions at present entertained 

 by some continental geologists on the subject, who 

 consider the muschelkalk as distinct from our lias ; 

 it has on the other hand been considered by some 

 geologists that the muschelkalk is a modification of 

 our lias, and that the quadersandstein* is the sand of 

 the inferior oolite ; conceiving it to be of some impor- 

 tance to determine if we are or are not to add two 

 new formations to our secondary rocks, I have, in an 

 Appendix, given the descriptions of these rocks by 

 Messrs. Humboldt and Boue, for the sake of com- 

 parison. With respect also to the identity of the 

 new red conglomerate with the rothe todte liegende 

 of Germany, it may perhaps be right to mention, as 

 discussions have lately taken place on this subject 



* This only refers to those localities where the sandstone thus termed 

 is distinctly interposed between the muschelkalk and Jura limestone, for 

 it is impossible to resist the suspicion, that more than one sandstone 

 formation has been confounded under this name in different districts. 



