IOWA ACADEMY OF 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, when, 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 whole 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. Evary hill is clay- capped, and every 

 clay-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 allavial 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, fire. 

 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 thejr have some special defense. This may be 

 found in one or both of two conditions; in a limited amount of 

 surface-moisture or ia lack of combustible material on the sur- 

 face of the ground. The alluvium offers both conditions; the 



