THE RHAETIC BONE BEDS 
217 
or pyritic, except when it occurs in or upon a sandy bed, 
when it is of the nature of a sandstone. A good example 
of this is seen at Lilliput^ — ^where it rests on Carboniferous 
limestone it is calcareous, but when on the Old Red, it is 
almost a sandstone. 
The animal remains are individual and separate, the 
occurrence of two or more bones, teeth, or scales joined 
together being extremely rare. Further, the bones are 
almost invariably broken or comminuted, a perfect bone 
(especially of the larger sizes) being seldom found. 
The usual idea that the bones are “ rolled ” is not borne 
out by close examination, especially of fresh or unweathered 
pieces. It appears to be founded on weathered speci- 
mens, or those which falling out of the cliff have been 
recently rolled about on the beach. This is the case at 
those three classic sections at Aust, Penarth, and Garden 
Cliff, where a considerable amount of weathering and water 
rolling has taken place. Another reason for the damaged 
appearance of the larger bones would be found in the 
vitriolic action of the iron pyrites, to which the larger 
bones, from their greater porosity, would be more vulner- 
able, many of them being quite rotten from this cause. 
Experience shows that the bigger the bone, the less chance 
there is of securing it in a decent condition. 
The teeth and scales, however, are mostly in a splendid 
state of preservation, all the delicate little points and 
markings being sharp and well defined, and exhibiting no 
trace of the wear and tear that “ drifted ” or “ rolled ” 
fossils ought to show. 
Further, the position these fossils occupy in the rock 
deserves attention. In a fairly tranquil or ordinary 
sediment tlie fossils usually lie on their flat sides, or on 
their longest axes, and are but rarely found at an angle or 
upright. But in a drift or storm deposit, on the contrary, 
the fossils are heaped up at all angles, and may frequently 
