PRELIMINARY NOTES ON THE ODONATA. 87 
ward to the Mississippi through valleys and entrenched meanders in 
the Cambrian strata from one to five hundred feet in depth. Its gorges 
and valleys are wildly picturesque and its general surface is flat or 
slightly rolling and covered with loess from the great river. 
In general, the highlands of the State lie in the central western 
part. The Leaf Hills of Otter Tail County have an elevation of 1,700 
feet and the prairie west of Itasca Lake in Becker County stands some 
1,600 feet. Irom this center arise three drainage systems of varying 
ages: the waters are carried northwestward by the tributaries of the 
Red River of the North and the Rainy River; to the southward and 
eastward by the Mississippi, the Minnesota and the St. Croix, and to 
the eastward in the northern portion by the smaller streams feeding 
into Lake Superior. The elevation of the northwest corner of the 
State is a little more than 750 feet, increasing in the southeast to 900 or 
1,000 feet. In the extreme southwestern corner, set off by the Coteau 
des Prairie, Rock and parts of Pipestone and Nobles Counties have an 
elevation of 1,800 to 1,900 feet, and drain to the southwest. 
Thus the central belt of the State is occupied by a great depression 
in which lie the valleys of the Red River of the North, the Mississippi, 
the Minnesota and the western half of the St. Croix, flanked by high- 
lands from 1,800 to 2,200 feet in elevation on the southwest and north- 
east. This depression marks the ancient outlet of glacial Lake Agassiz. 
If we now turn to the life zones, we immediately note their coin- 
cidence with the topographic features. The boundary between the 
Canadian (the lower division of the Boreal Region) and the Transition 
(the upper division of the Austral Region) Zones enters Minnesota in 
Pine County on the east, near the head waters of the St. Croix, and 
passes westward through Mille Lacs to the junction of the Crow Wing 
River with the Mississippi, hence northwestward between Leech and 
Itasca Lakes, west of Red Lake and into Ontario to the west of Lake 
of the Woods. On the south, the boundary line separating the Transi- 
tion from the Upper Austral (Alleghanian) bisects Houston County 
from north to south, meanders through the two northern tiers of coun- 
ties in Iowa and again enters Minnesota in Nobles County and fol- 
lows the Coteau des Prairie into South Dakota. Thus the northeastern 
third of the State belongs to the Canadian, a fragment of the south- 
western to the Upper Austral and the whole central belt of valley land 
from northwest to southeast, 800 to 1,200 feet below the highlands, to 
the Transition Zone. 
The region thus covered by the Transition, or Alleghanian Zone 
includes four topographic types. The areas drained by the Red River 
and the Minnesota are markedly prairie and constitute the richest farm 
