278 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
Grease wood will not burn freely, owing to its being a sparse growth j 
and as the Rocky Mountain locust does not frequent the cold, clayey 
soils which produce this plant, such regions are of no importance in 
ili is connection. • 
Timbered lands are not considered in this connection, as these insect* 
do not breed in a timbered country. 
The great area of the plains, stretching eastward in a long inclined 
plain from the base of the Rocky Mountains, is therefore mainly cov- 
ered with grasses, which are mostly low, seldom forming a sward but 
growing in bunches or tofts. 
In the British Possessions the area of the plains, or level, untimbered 
regions, is divided by Mr. Dawson, the Canadian geologist, into three 
" prairie levels " or steppes — steppes with very slight rise and long trend. 
The first of these includes the region of the Lakes Winnipeg, Manitoba, 
Winnepegosis, &c. It is heavily timbered, except near its western 
border. Its mean elevation is not far from 1,000 feet. Eising from 
this, westward, iu bluffs two or three hundred feet in height, is the 
eastern escarpment of the second prairie level, of which the Coteau des 
Prairies, in Minnesota, is the southern extension. This is tolerably fer- 
tile, well grassed, with timber only in the bottom lauds of the streams and 
on knolls and the faces of bluffs. Its elevation is from 1,200 to l,50O 
feet above the sen. gradually rising westward. The third prairie level 
is what corresponds, in the United States, to the plains proper and the 
Coteau du Missouri. It rises from the last in ill-defined bluffs, of 
small height. From the edge it gradually increases iu height westward 
until, at the base of the Pocky Mountains, it is 4,000 to 5,000 feet above 
the sea. On this level the grass is shorter, less luxuriant, and in some 
places, especially near the boundary, shows the effect of a climate de- 
cidedly arid by the presence of sage and cacti. Timber is distributed 
very much as on the second level, but is decidedly more scarce. 
As we proceed northward over the two upper prairie levels in the 
country between the forks of the Saskatchewan, the climate becomes 
moister with the increasing cold, and the vegetation approaches more 
and more the nature of that on the true prairies of the Mississippi Val- 
ley; and north of an undulating line which follows approximately the 
course of the 52d parallel, patches and belts of timber begin to diversify 
the surface, alternating with the rich grasses. The change from prairie 
to forest goes on gradually over a belt 50 to 75 miles in breadth, and 
the North Saskatchewan is reached before the forest has asserted solo 
proprietorship. South of Belly Eiver, more arid conditions manifest 
themselves. At the base of the Pocky Mountains, and indeed for a 
hundred miles eastward, and about the Judith and Big Horn Ranges, 
the influence of the mountains in inducing a moister climate is plain; 
the grass is tolerably luxuriant everywhere, and especially so at the 
base of these ranges, gradually shading off in luxuriance with the dis- 
tance from them. 
