THE CAMBRIDGE GREENSAND. 593 
portions of skeletons of single animals, and that scattered or 
isolated bones are comparatively rare. It rarely happens that any 
pit yields more than three or four skeletons. These are almost 
always of different species; they generally occur at considerable 
intervals of time; and if an animal happens to lie in the line in 
which the rock is being worked its remains are collected in a few 
minutes, while if it is at right angles to the working it will have to 
be watched for bit by bit as the excavation progresses. In ar- 
ranging these Dinosaurian and other fossils in the Woodwardian 
Museum, I have occasionally had to reject an accidental Ichthyo- 
saurian or Plesiosaurian fragment found with a Dinosaur; but I 
hardly ever remember evidence of two Dinosaurian skeletons being 
mixed together. And when this has occurred the circumstance 
could be traced to the fossils having been indiscriminately purchased 
and mixed by the engineer at the works, or only collected after 
having been triturated in the mills. 
There is no doubt that some of the bones in the Cambridge 
Greensand have suffered from attrition, and it is probable that the 
apparently worn condition of the bones has led to the belief that 
they were derived from some older formation ; but not only is a 
similar fauna unknown in any older formation, but it occurs well 
developed on this horizon at Gosau, in Austria. Moreover, the bones 
are much less worn than is often the case with specimens from the 
Wealden deposits of Sussex ; and no one has ever suggested that the 
Wealden fossils are derivative. And in so far as the Cambridge 
Greensand specimens are worn, it is probable that the greater part of 
the abrasion has been produced in the washing-mills at the several 
diggings after the specimen had been dug out from the bed. In 
many cases, however, this explanation will not apply; and bones 
occur which have roughened edges, roughly fractured surfaces, and 
considerable holes penetrating into their substance. These circum- 
stances led me to institute experiments on the effects of exposure of 
bones to the air and subsequent maceration as influencing their con- 
dition of preservation ; and I have found the articular ends especially 
to suffer from exposure, while under maceration the bones become 
so brittle that they are fractured with slight movement. In the 
case of land animals, such as Dinosaurs, both these conditions may 
well have exercised an influence; and what has hitherto been re- 
garded as evidence of wear scems to me better explained in this 
way. Many associated bones are decomposed, past all recognition, 
on the exposed neural surfaces; while the ventral surfaces which 
rested on the sea-bed yield valuable distinctive characters. 
I yenture now to submit to the Geological Society some account of 
the structure, affinities, and systematic position of this Dinosaurian 
fauna ; and I desire to express my grateful sense of the kindness of 
Prof. Hughes in affording me facilities for studying the Wood- 
wardian Dinosaurs, and my indebtedness to the Council of the Royal 
Society for assistance in carrying on this investigation. On the 
present occasion I offer descriptions of a few only of the typical 
Dinosaurs of the deposit. 
