IOWA ACADEMY OP SCIENCES. 57 



and western parts of the state are, however, more general. 

 The greater scarcity of timber in the west is in all probability 

 due chiefly to the stronger, hotter and drier winds, to the south- 

 west course of the river valleys, whose bluffs, therefore, offer 

 but little shelter to trees, and to lesser rainfall. That wind, 

 however, is primarily responsible is shown by the difference 

 between the Iowa and Nebraska bluffs along the Missouri river. 

 These bluffs have substantially the same amount of rainfall, 

 etc. , but differ in exposure to the southwest winds. 



That artificial groves often survive, and even thrive, on the 

 prairies is due to the care which they receive. Cultivation, 

 replanting, general care, and massing in groves often improve 

 the conditions to such a degree that the unfavorable influence 

 of wind is counterbalanced. But neglected groves, when 

 exposed, soon deteriorate, and finally perish. 



******** 



Incidentally, an application of this view of wind action may 

 be made to another question of interest. It has already been 

 noted that in eastern Iowa the forests are chiefly on loess which 

 here mantles the hills with nearly uniform thickness. It was, 

 therefore, assumed, that trees found loess especially suitable 

 to their growth. However, in western Iowa the loess hills, 

 covered more irregularly with a much thicker deposit, are in 

 large part devoid of trees, while on the other hand drift ridges 

 often have more or less timber.* 



It is noticeable, however, that in the drift area where groves 

 have gained a foothold a thin veneer of loess-like material, 

 varying from one to two feet in thickness, is found. This is 

 true even of the scrub oak groves on the northeast slopes of 

 the drift hills in western Lyon county, — a fine soil occurring 

 in the groves, while on the south and west the ridges are 

 gravelly at the surface and treeless, f 



It would seem then that the mere presence of loess does not 

 insure abundant native timber, and that trees may gain a 

 foothold upon drift. In fact the drift-covered area is 

 often capable of sustaining a remarkable growth of trees, the 

 artificial groves near Sibley being a fine example. Some years 

 ago the author suggested J that the loess instead of causing or 

 favoring growth of timber, is rather a wind deposit collected 



* As near Forest Olty, at Olear Lake, etc. 



+See the author's discussion of surface deposits already noted. 



*Proc. Iowa Acad. Scl., Vol. Ill, pp. 82-89, 1895. 



