ROOM IV. STATE OF PRESERVATION OF ENALIOSAURIANS. 369 



contain a greater number, and more perfect skeletons of sau- 

 rians, than others. The uppermost beds consist of Alum shale, 

 with a profusion of ammonites and crinoidal remains. The 

 next subdivision comprises strata of marlstone and blue marl, 

 in which bones of Enaliosaurians are but rarely met with ; 

 but ammonites, belemnites, and other cephalopoda, and the 

 usual marine shells and zoophytes of the Liassic formation 

 are abundant. 



The next group, the limestones, is the grand depositary of 

 the reptilian remains, " the inestimable treasury of the most 

 splendid epoch in the physical records of our planet." l Some 

 of the thin intermediate layers of stone are, however, literally 

 a mass of pentacrinites, and others are wholly made up of 

 ammonites ; the organic remains being^ more or less mineral- 

 ized by pyrites. 2 



The most beautiful and perfect examples of Plesiosauri and 

 Ichthyosauri collected by Mr. Hawkins, were extracted from 

 these strata. The total thickness of the limestones, and al- 

 ternating layers of marl, at Kingston, near Street, is about 

 twenty feet ; at Lyme Regis (forty miles from Street), the 

 section east of Church Cliff, is thirty feet thick. 



A bituminous marl, of a black colour, the last deposit in 

 the series, contains similar remains with the limestones ; and 

 in addition, some fossil terrestrial vegetables not observed in 

 the other strata- 3 



At the base of the Lias, and separating the lowermost shale 

 from the uppermost Triassic bed beneath, there is a layer of 

 coarse detritus, a few inches thick, commonly known as the 

 Bone-bed, composed of mud and sand, and the debris of 

 fishes and reptiles. 4 



STATE OF PRESERVATION OF ENALIOSAURIANS. The remark- 

 ably perfect state of the skeletons of the Plesiosauri has 

 already been pointed out ; many of those of the Ichthyosauri 

 are equally entire. In several of the specimens in the Museum, 

 the bones are seen in all their integrity, as in recent anatomi- 



1 Mr. Hawkins's Memoir, p. 5. 



2 Specimen of Pentacriniles from these strata are deposited in "\Vall- 

 case G, Koom II. see ante, p. 74. 



3 Mr. Hawkins's Memoir, p. 7. 



4 See " Wonders of Geology," p. 529. 



B B 



