228 '/'//' American Geologist. October, 1894 
is probable also that this broadening of the lands by elevation 
and coast building, by extending the field for land organisms, 
was favorable to the great group of reptiles. We find a par- 
allel development of the group of mammalia when in the suc- 
ceeding Tertiary periods the lands again became the present 
massive continents. 
Objections arising from lack of knowledge <>J' the distribu- 
tion of the Mesozoic reptiles. It is not too much to say that 
existing reptiles are lowland forms. While a few specie- 
range to great altitudes they are so few in numbers individu- 
ally and specifically as to detract nothing from the generali- 
zation. It is. however, much more difficult to substantiate 
this claim for the class in Mesozoic times. With the great 
diversity of reptilian life which then existed it is highly 
probable that forms were adapted to life in mountains as well 
as on the plains. We should expect from the affinities of the 
dinosaurs and what can be learned of their habits that the}' 
were water-loving forms, and hence ranged along the rivers 
and lake basins. Professor Marsh speaks of the Atlantosau- 
rus as inhabiting the shores of the mountain lakes; but the 
bulk of this and other animals of the order makes their dwell- 
ing in a strictly mountainous region quite improbable. It 
seems more likely that the kangaroo-shaped dinosaurs, par- 
ticularly such forms as Claosaurus, Ceratosaurus, or even 
Anchisaurus of the Jura-Trias, were adapted for progression 
over plains. But although the variety of forms was carried 
to such an extent, with adaptations to every habitat and sta- 
tion, there is little question, it seems to me, that the class was 
then as now mainly distributed in the lowlands. 
Mammalian life unfavorably affected by the peneplain <in<] 
reptilian life. 
The weak marsupials or low mammals, which first appear 
in this country with Dromatherium in the tolerably high relief 
of the Trias, were apparently driven to the uplands by the 
more puissant and numerous reptilia of the peneplain. Their 
development seems also to have been retarded. This restraint 
of the higher elass by the reptilia we may fairly attribute to 
the advantage which the latter derived from favorable geo- 
graphic conditions. "It is a most remarkable fact,'" says 
LeConte, "that although marsupial mammals have been found 
