IOWA ACADEMY OP SCIENCES. 
99 
very near the truth each of them in his theory missed the mark. 
It remained for an almost lifelong resident of the prairie, a 
former active member of this academy, to study to better pur- 
pose, Iowa’s forest distribution, w^hen, as a vigorous geologist he 
made his now famous pilgrimage through our eastern counties. 
Mr. McGee was quick enough to notice that the soils of our 
prairie region are indeed peculiar, and of several sorts, and 
that the vegetation varies with the soil, but he went farther: 
he referred the v/hole problem back to conditions geological, to a 
situation resultant from the nature and manner of the latest 
geological deposit. The soils of Iowa are three, the drift of 
the prairie, the loess of the hills, the alluvium of the river 
flood- plains, and Mr, McGee’s contribution to our problem 
lies in his emphasizing the fact first noticed by Whitney, that 
the forests and groves of Iowa, except where alluvial, are 
everywhere coterminous with the distribution of the loess. 
Since Mr, McGee has called attention to the fact, of course, 
everybody sees it. The merest tyro in such studies has but to 
drive across some eastern county of our state to see how very 
striking the relation is. Every hill is clay- capped, and every 
cla^T-'Capped ridge is covered with woods. Sometimes the clay 
is replaced by sand, but the woods cover the sand, as Whitney 
says, just the same. 
There is one other fact, however, to which attention has not 
yet been called, which has a distinct bearing upon our problem 
and that is the fact that subsequent to the occupancy of the 
state by civilization the forest began slowly to enlarge. Many 
localities might be cited in proof of this statement. I have in 
mind one field of thirty acres in 1844 cultivated as a cornfield, 
now used year after year as a grove for Fourth of July cele- 
brations. Then again, as Whitney remarked, trees grow on all 
the alluvial soils of Iowa, so that outside the fact of soil-differ- 
ence, there must be still a factor operating to make the differ- 
ence in soil efficient. That factor in my opinion is that already 
mentioned as of universal popular appreciation, namely, Jire. 
Fires have prevailed on the continent not only for generations 
as man reckons the years, but for forest-generations for hun- 
dreds and hundreds of years. In the presence of fires forests 
endure only as they have some special defense. This may be 
found in one or both of two conditions; in a limited amount of 
surface- moisture or in lack of combustible material on the sur- 
face of the ground. The alluvium offers both conditions; the 
