THE AVON AND ITS GRAVELS 
239 
hicornis. They have the following points in common : 
1. They have two fronto-nasal bones. 
2. They have no functional incisors when adult. 
3. A buttress common on the molars of other forms is absent from 
these. 
4. There are three digits on the manus. 
5. They are highly specialized. 
The present distribution of the genus Rhinoceros is 
interesting. To-day it is confined to the warmer 
parts of Asia and Africa. The genus includes five well- 
marked species, one of which (R. simus), the large flat- 
nosed African form, is now probably extinct. The other 
African form is R. hicornis. The three Asiatic forms are 
R. unicornis and R. sondaicus, both of which are one- 
horned, and R. sumatrensis, which is two-horned and the 
smallest of the group. 
In Miocene times the Rhinocerotidm were well repre- 
sented in both old and new worlds, though in America 
they became extinct before the end of the Pliocene. 
Judging from the abundance of their remains and from 
the unspecialized forms found in the Eocene of the Rocky 
Mountains, it has been inferred that they originated in this 
region. Three species are believed to have inhabited the 
Rritish Isles, of which R. tichorinus is the most familiar. 
Other finds include a horncore of Bison priscus, with its 
characteristic longitudinal furrowing, and teeth and 
other parts of Equus. The paleontology, however, of the 
gravel is so rich and interesting that it deserves a separate 
paper, and has only been introduced here as an aid in 
determining the age of the Avon. 
In conclusion, the main points of interest may be sum- 
marized as follows : — ■ 
1 . The western part of England was elevated before the 
■eastern ; the Avon has therefore been longer at work than 
the Thames throughout its entire course. 
2. The denudation of these valleys was far advanced 
in glacial times. 
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