446 Mr. De la Beche's Sketch of a Classification 



in determining the relative ages ©f this and the previously no- 

 ticed group in cases where the niineralogical structure is of 

 no avail. 



Group 5. {Oolitic) comprises the various members of the 

 oolite or Jura limestone formation, including lias. The term 

 oolitic has been retained upon the same principle as that of 

 cretaceous : in point of fact even in England and the North of 

 France the oolites, properly so called, form but an insignificant 

 part of the mass of rocks known by the name of the oolite for- 

 mation; this character is also not confined to the rocks in ques- 

 tion, but is common to many others. In the Alps and Italy 

 the oolite formation is replaced by dark and compact marble 

 limestones, so that its niineralogical structure is of no value. 

 Saurians would appear to have been abundant in some places. 

 The prevailing fossil characteristic seems the extraordinary 

 quantity of ammonites and belemnites, the remains of which 

 are so numerous in this group. It is remarkable that the 

 nautilus should have been continued down to the present time, 

 and that the other camerated shells which swarmed at this 

 epoch should not now be found. The belemnites do not ap- 

 pear to occur beneath the lias, at least as yet we have no well 

 authenticated instance of such occurrence. 



Group 6. {Red Sandstone) contains the variegated marls 

 [Marnes irisees, Keuper) the Muschelkalk, the New Red Sand- 

 stone [Gres Bigarre, Bunter Saiidstein), the Zechstein, and the 

 Exeter Red Conglomerate [Rathe Todte Liegende). The whole 

 is considered as a mass of conglomerates, sandstones, and marls, 

 generally of a red colour, but most frequently variegated in 

 the upper parts. The limestones may be considered subordi- 

 nate. Sometimes only one occurs, sometimes the other, and 

 sometimes both are wanting. There seems no good reason for 

 supposing that other limestones may not be developed in this 

 group in other parts of the world. When the muschelkalk is 

 very compact with broken stems of the lily encrinite *, one of 

 its characteristic fossils, it might easily be mistaken for some 

 of the varieties of the carboniferous limestone. In some places 

 the new red sandstone contains an abundance of vegetable re- 

 mains, at others none can be detected in it. The saurians first 

 appear in the ascending series, at least in any abundance, in 

 this grouj). As I have before observed, the lower part of this 

 group generally rests unconformably on the inferior rocks, and 

 seems to liave resulted from a very general upheaving and frac- 

 ture of (he preexisting strata, accompanied by the intrusion of 

 trap rocks. 



* Encrinites moniliformis. Miller. 



Group 



