22 IOWA STUDIES IN NATURAL HISTORY 
ed here, although/unsatisfactory in many respects, affords the 
best logical rough divisions from the viewpoint of the animal 
life. No attempt has been made to take into consideration all 
the species of trees, but the classification has been based upon 
the predominating species. Even this presents difficulties, par- 
ticularly in the case of the oaks, of which there are some half 
dozen species common in the county. The oak formations vary 
from the burr oak and red oak common on the higher grounds to 
the mixture of swamp oak, pin oak, and shingle oak, respectively, 
among other trees on the low grounds of alluvial formation. 
While each of these several species must have its own particular 
parasites, yet the insect forms, such as borers, feed more or less 
indiscriminately upon all species of a single genus. 
For the present purposes the forested lands have been elassi- 
fied as follows with reference to the predominating species: 
(1) oak; (2) oak-hickory; (3) elm (on the alluvial land of the 
larger streams usually mixed with cottonwood, box elder, soft 
maple, hawthorne, ete.); (4) willow; (5) hazel; (6) miscella- 
neous thickets; (7) cleared land on which the stumps remain. 
The extent and area of all these is shown upon the separate 
township maps, Plates IV to XXIII. Cross hatching, both hori- 
zontally and vertically, of any area indicates that there is abun- 
dant underbrush also present. | 
(1) Oak. As indicated in the general discussion, the oaks 
alone present a widely varying series of conditions, both as to 
distribution and as to species. Disregarding these factors in this 
preliminary survey, it has been considered necessary to make 
some further classification of the oak formations. Briefly, these 
are scattered oak groves, quite uniformly in pastures, oak timber 
free from underbrush (due also to pasturing), and oak timber 
with abundant underbrush. On the township maps, all oak has 
been represented by irregular O-shaped marks. The scattered 
characters indicate scattered oak, the characters upon horizontal 
ruling indicate oak timber, and when cross-ruled means oak tim- 
ber with underbrush. As will be seen, for example in Section 31, 
Fremont township, the oak frequently merges into other forma- 
tions. The O-shaped character in conjunction with solid black 
triangles indicates oak-hickory. 
