of European Rocks. 155 



it cannot be imagined that all the waters of the globe became 

 suddenly fresh in order that these rocks might be formed, 

 and as suddenly salt again for the deposition of the green- sands 

 and chalk. Some French geologists moreover consider that 

 in France there is a marine equivalent of the Wealden rocks. 



As far as our observations of fossil organic remains have 

 yet extended, it would seem probable that the ammonites and 

 belemnites ceased to exist after the formation of this group ; 

 for, as yet, their remains have not been detected in Group 3. 

 Should this, after a greater extent of the world has been ex- 

 amined, be found generally true, it will be a most valuable 

 guide in determining the relative ages of this and the pre- 

 viously noticed group, in cases where the mineralogical struc- 

 ture 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 insignifi- 

 cant part of the mass of rocks known by the name of the 

 oolite formation; this character is also not confined to the 

 rocks in question, 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 mineralogical structure is of no 

 value. Saurians would appear to have been abundant in some 

 places. The prevailing fossil characteristic seems the extra- 

 ordinary 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 

 appear 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 Sandstein), the Zechstein, and the 

 Exeter Red Conglomerate (Rothe Todte Liegende). The whole 

 is considered as a mass of conglomerates, sandstones, and 

 marls, generally of a red colour, but most frequently varie- 

 gated in the upper parts. The limestones may be considered 

 subordinate. Sometimes only one occurs, sometimes the other, 

 and sometimes both are wanting. There seems no good rea- 

 son for supposing that other limestones may not be developed 

 in this group in other parts of the world. When the muschel- 

 kalk is very compact with broken stems of the lily encrinite*, 

 one of its characteristic fossils, it might easily be mistaken 



* Encrinites moniliformis. Miller. 



