THE BONE-BED AT AUST, NEAR BRISTOL. 



415 



time Mr. Charles Moore, in an elaborate series of papers*, has 

 proved with extreme minuteness and care that there extended over 

 the Somersetshire and South Wales Coal-fields, and over the 

 Mountain Limestone, beds containing Rhsetic fossils, the crevices, 

 veins, and pot-holes in the Mountain Limestone being filled up with 

 orgauic reliquiae of vertebrates as well as invertebrates of Rhsetic age. 

 These, according to Mr. Moore, have been washed in during the Ehselic 

 and subsequent Liassic periods. Such being the case, the circumstances 

 attending their deposition warrant the supposition that some of the 

 fossils included in the Rhaetic deposits were derived from the 

 disintegration of the rocks on which they now rest. The bone-bed is 

 variable in thickness, but rarely exceeds a few inches ; at Aust it is 

 from 3 in. or 4 in. to 9 in. thick ; in many other places it is less, 

 ranging over considerable areas with a thickness not exceeding one 

 inch. There is also much diversity in the prevalence of organic 

 remains. In a few localities the fish-remains occur in abundance, 

 as at Aust, Axmouth, Coomb Hill, &c, whilst in other places they 

 are entirely absent or are found very sparingly. 



The fishes found in the bone-bed are comprised in the orders 

 Plagiostomi and Ganoidei, the latter including, according to 

 Prof. Miall f, the Ceratodus-rem&ms. Besides Ceratodus, the Ganoids 

 include the genera JSaurichthys, Gyrolepis, Lepidotus, and Ambly- 

 pterus. 



Amongst the Plagiostomous genera may be enumerated Hybodus, 

 Acrodus, Sargodon (?), Nemacanthus, SpJienonchus, Lophodus, Sqiialo- 

 raia. 



There are also large numbers of bones, teeth, and other remains 

 of Saurians, including Ichthyosaurus, Nothosaurus, Scelidosaurus, 

 and others found and identified by Mr. Moore J. 



A consideration of the characteristics of this mixed group of 

 organic remains may afford some reasonable basis for deductions as 

 to the circumstances under which they were accumulated. The 

 Saurians would undoubtedly exist near and partly on land. The 

 Ceratodonts, judging from a comparison of the forms of their teeth 

 with the still existing Ceratodus of Australia, were vegetable 

 feeders, and would require a shallow-water area from which to 

 obtain their food. With respect to the remaining Ganoids, it is 

 probable that they could freely exist in deeper water, and, from 

 the character of their teeth, were probably predaceous in their 

 habits. The Plagiostomous Sharks, with their sharp teeth and 

 strong fin-spines, often attaining a large size, as evidenced 

 by the great length of the latter, would be equally adapted 

 for either deep or shallow waters. Taking all the items 

 together, it would appear that the Phsetic beds were deposited in 

 a shallow sea not far from the coast ; that the Saurians passed a 

 large proportion of their existence in the water, the remainder on 



* Quart. Journ. Geol. Soc. vol. xvi. p. 483 (1860), vol. xxiii. p. 449 (1867), 

 vol. xxxvii. p. 67 (1881). 



t Palaeontographical Soc, vol. xxxii. (1878). 

 \ Loco. citt. 



