246 NEW RED SANDSTONE. 



moment so long as the latter are regarded as Passage Beds ; for 

 such beds may naturally have a greater analogy with the over- 

 lying beds in one locality, and with the underlying beds in 

 another.^ 



No doubt the Grey Marls, as a mass, mark some general change 

 in the character of the sediments, which came on gradually and 

 without any approach to uniformity. Were their colour due 

 simply to superficial weathering or discolouration of Red Marls, 

 we should expect the exposed surfaces of the Keuper Beds to be 

 generally of a grey tint, which is not the case. The Grey INIarls 

 have yielded one fossil of the highest interest, namely a tooth of 

 the oldest known British Mammal, Mkrolcstes {Hypsiprimnopsis) 

 Rhceticus, which was found by Prof. W. Boyd Dawkins at Watchet.^ 

 Fish-scales have also been recorded from marly limestones below 

 the Black Shales at Penarth, and at Milton Lane, near Wells.^ 



The evidence afforded by the Fish-remains which occur in the 

 Bone-bed would incline us to connect the Rhastic Beds with the 

 Trias ; for, as Sir Philip Egerton pointed out, some forms are allied 

 to and some are identical with Muschelkalk species.'' Hybodus and 

 Acrodus are, however, common both to the Keuper strata and to 

 the Lias. The Mollusca serve to link the Rhaetic Beds with the 

 Lower Lias, from which, nevertheless, they are distinguished in 

 this country by the absence of Cephalopoda ; no species of 

 Ainmonitcs or Behmriites being known from the beds. 



In any case we may look upon the Rhcetic Beds as forming the 

 connecting link between the New Red Sandstone and the Jurassic 

 strata, a fact of much interest considering the different physical 

 conditions under which these two great systems of strata were 

 deposited. Edward Forbes, many years ago, expressed the opinion 

 that the fossils of the White Lias were curiously representative of 

 the existing Caspian fauna. He then broached the notion that 

 the Red Marls were formed in a great salt inland sea (a sort of 

 Aralo-Caspian), during the last state of which, probably during 

 influxes of the sea, the White Lias was formed : and that the area 

 was subsequently depressed and turned into a part of the ocean, 

 when the Liassic fauna came in.^ In their method of formation 

 the Rhaetic Beds may thus, on the whole, be closely related to the 

 Trias, and we may include them in that division as the uppermost 

 member of the New Red Sandstone or Poikilitic System. 



The Rhaetic Beds have been found between the Red INIarls and 

 the Lower Lias, wherever sections have been exposed. They may 

 therefore be said to extend across England from near Redcar on 



1 Prof. E. Renevier, Bull. Soc. Vaudoise des Sc. Nat. viii. 39 ; see also Prof. 

 R. Tate, Geol. and Nat. Hist. Repertory, i. 364. 



- Q. J. XX. 396 ; see also Q. J. xii. 252. 



^ Vertical Sections, Sheet 46 (Geol. Survey). 



* Proc. G. S. iii. 409 ; see also J. W. Davis, Q. J. xxxvil. 414. 



■'• Memoir of E. Forbes, by G. Wilson and A. Geikie, 1861, p. 41S ; Ramsay, 

 Q. J. xxvii. 189. 



