THE LIFE Of MAMMALS 
the front in an astonishing outburst, as it may be fairly called [so that the 
Tertiary is styled Age of Mammals]. Henceforth the mammals were to 
be the dominating type, taking the place of the dethroned species. 
“Much of mammalian history has been preserved in the fresh-water 
deposits of Tertiary age in various parts of the world, but in no region yet 
Age of known with such fullness as in the western part of the United 
Mammals. States, where are found deposits covering almost the whole 
of Tertiary time. These great rock masses, of different dates, cover thou- 
sands of square miles, and were laid down in various ways. Some were 
accumulated in lake basins, others were spread by sluggish streams over 
their flood plains, others may have been heaped up by the winds in 
semi-deserts. The rocks thus accumulated entombed the bones of innu- 
merable animals, the fossil remains of which are not only extraordinarily 
abundant, but are preserved in a degree of completeness found in very few 
other parts of the world.” 2” 
Notre. — The small raised figures in the text refer to the enumerated 
List of Authorities at the end of the book. 
Technical (specific) names will be given, so far as it seems desirable, 
in the Index. 
SKULL OF SIVATHERIUM, 
