I860.] WEIGHT LIAS AXD BONE-BED. 409 



that the Avicuxa contorta beds, which he at the base of the Lias, 

 contain a fauna of a special character; several of the Conchifera are 

 identical with species found only in the Upper St. Cassian beds and 

 Kossener-Schichten of continental geologists. These remarkable 

 strata are grouped by one class of observers with tho Trias, by 

 another with the Lias ; the difference of opinion among continental 

 geologists has arisen from the circumstance that the majority of the 

 species have a Triassic fades, whilst a few only are said to pass into 

 the Lias. 



In England, on the contrary, our grouping of tho Avicula contorta 

 beds has been based chiefly on their lithological character ; and in 

 part likewise from their being fossiliferous, and resting on the upper- 

 most part of the iinfossiliferoiis lied Marl ; the fossils they were 

 found to contain being assumed to be Liassic, from their proximity to 

 the fossiliferous beds of the Lias. 



It has been stated by Sir Philip Egerton and Professor Agassiz, 

 that the Pishes of the English Bone-bed are either special to that 

 breccia, or belong to species which are well known in the Muschel- 

 kalk of Germany. General Portlock, who found these beds in the 

 North of Ireland, stated that they contained Muschelkalk fossils ; and 

 Sir Charles Lyell, in his 'Manual,' from the determination of the Fish, 

 placed the Bone-bed in the Trias. Lastly, I have now shown that 

 the Conchifera are special to this zone, and that none of them ap- 

 pear to pass into the true Lias. 



The Avicula contorta beds occupy a considerable area in the Mid- 

 land Counties, the South of England, and South Wales, and through- 

 out present very uniform lithological and palseontological characters ; 

 General Portlock having found them in the North of Ireland, and 

 Mr. Howell at Bagots Park in Staffordshire, whilst I have traced 

 them through the counties of "Worcester, Warwick, Gloucester, So- 

 merset, Glamorgan, and Dorset. 



Whatever may be determined regarding the true grouping of the 

 Avicula contorta beds, there can lie no doubt that theZoxB of Ammo- 

 nites PLAHOBBIB belongs to the Lias, and forms the base of that for- 

 mation, should the Avicula contorta beds be hereafter removed to 

 the Trias. This zone is remarkable for && first a/ppearanct of Am- 

 monites under the simple form of Ammonites planorbia in some of its 

 lowest beds, where they appear sparingly. Tiny are abundant in the 

 tipper shales, where the species become extinct. The Am.planorbis 

 beds may be described as the firsi Saurian zone of the Lias, if the 

 Hi hi i '-lied be removed from this formation. Plesiosaurus megacepTialus, 

 J'. Etheridgii, P. Hatvhinrii, and P, dolichodeirus are found in the 

 Lower " Fire-stones ;" and Ichthyosaurus intermedius and /. tenui- 

 rostris in the shales and limestones above these, [nsects are found 

 in different beds in this cone in some localities, and only in one or two 

 limestone-beds in others. The thin laminated shales are often much 

 marked by rain-spots. These facts attest the marginal nature of 

 these deposits. The numerous Sea-urchins of the " Guinea-bed " 



and the Corals of the other strata prove that marine life there pre- 

 vailed. 



vol. xvi. — PASS I. 2 B 



