84 
Mr. Clift on some fossil bones 
and on its elevation, and different degrees of moisture at dif- 
ferent periods ; and perhaps, in a great measure on the den- 
sity or compactness of the bones themselves. There are 
specimens in the Museum of the College of Surgeons, of sec- 
tions of teeth of the animal incognitum, or mastodon, from 
the blue clay on the banks of the Ohio ; and of the bear from 
the caverns at Gaylenreuth, which have retained their ani- 
mal matter so entirely, as to preserve their form most per- 
fectly, after having been deprived of their earth by means of 
muriatic acid, while, under other circumstances, teeth and 
bones of the densest kind, lose their cohesion immediately 
after being exposed to the air, and becoming dry. This is 
constantly the case with the tusks, molares, and other bones 
of the elephant, so frequently found in the yellow sand above 
the blue clay at Brentford, Ilford, and other situations in the 
vicinity of the River Thames ; which invariably separate into 
small lozenge-formed or cubic fragments as soon as they 
become dry. 
On immersing the bones of the carnivorous animals in 
water, more effectually to remove the clay without injuring 
the surface, they effervesced strongly, and became nearly of 
a black colour, but recovered their former appearance on 
drying. A similar effect was produced, but in a less degree 
as to colour, on the bones of the bovine animals, and of the 
horse. 
It may be worthy of remark, that appearances of disease 
in fossil bones are of rare occurrence ; and I have never yet 
seen an instance of fracture that had been united during the 
life of the animal : but among these occur two examples in 
the metacarpal and metatarsal bones of the bovine animals, 
