22 INTRODUCTION. 



tinents. There there are traces of many animals that 

 do not now exist, but which have certainly existed 

 along with the races that now inhabit the same regions, 

 because their remains are found together in collections 

 of matter that have not been subjected to any other 

 change than that produced by ordinary accumulation. 

 Besides those animal remains that are imbedded in the 

 different strata of rocks, and among which, though 

 care must be taken not to confound skeletons that are 

 more changed and mutilated with animals originally 

 less perfect, there is a sort of progressive character 

 from simpler to more complex. There are animals 

 which, from the situations in which their remains are 

 found, cannot have been extinct anterior to any great 

 or general revolution of the globe. Of these, the most 

 remarkable are a species of elephant, one of rhinoceros, 

 and one of hippopotamus, which appear to have been 

 pretty generally diffused over the cold, or at least the 

 temperate parts of the northern hemisphere. The 

 tusks, teeth, and other bones of an elephant, are found 

 in soft deposits, such as clay, mud, and marie, or under 

 peat-bogs. They have been found in many parts of 

 England, in Scotland, and in Ireland ; and the remains 

 of the rhinoceros and hippopotamus are found in the 

 same kind of situations. In the clay formation at 

 Brentford, in Middlesex, at no very great depth below 

 the surface, we believe the remains of all the three have 

 been met with ; and from their being found near 

 situations which are frequented by the living species of 

 accompanying fossil animals, and also in many stages of 

 their growth, there remains not a doubt that they sub- 

 sisted in the districts that now contain their bones. 



