i^'26 Miscellaneous, 



provinces, assisting to determine where it would be eastward were 

 it not disguised by local irregularities of surface. 



The cause of the disappearance of trees in the Campestrian 

 Province is, in a word, the deficient and irregular supply of mois- 

 ture. I need not enter into the proofs of this, but refer to the 

 records of meteorologists. It is true that this does not materially 

 affect agriculture in the more eastern regions ; in fact, most crops 

 will succeed better with less rain than is necessary for most trees 

 to thrive, and in some years there is even a greater supply ot rain 

 in the Texan and Illinois regions than eastward. But there are 

 years and series of years of drought, when in their natural con- 

 dition the forests take fire from the slightest cause and burn over 

 large tracts. This was made even more general by the Indians 

 but since the white settlement has in great degree ceased and 

 forests have been re-established. In the Apalachian region 

 droughts have never been sufficient to keep trees from extending 

 themselves as soon as a forest might be partially destroyed by fire, 

 and thus the formation of prairies has been prevented. A consi- 

 deration of the source of the rains will explain why the limit of 

 prairies has its present direction. Coming north from the Gulf 

 they are continually carried more and more eastward by the west- 

 erly winds ; and as the greater part of the moisture is precipitated 

 before reaching the Ohio river, the Illinois region is deprived /or 

 man^ years of its due share of rains. 



The Texan region lying quite west of the line of travel of those 

 Gulf streams has to depend on less abundant sources for its rains. 

 Now, as we go westward the supply rapidly diminishes until in 

 the Camanche and Dacotah regions it is entirely inadequate to 

 the growth of trees as well as of most cultivated products ; and in 

 some parts even grass and other herbage entirely disappear over 

 vast tracts. From the great bend of the Missouri north, however, 

 there seems to be an improvement in the country. On the banks 

 of that river, above Fort Union, there is no long interval without 

 trees as there is farther south on nearly all the streams, and on 

 the Saskatchewan there is even less. 



The very porous character of the soil and underlying rockg 

 assists much in this aridity of the country, and we therefore find 

 that the line marking the junction of the carboniferous rocks of 

 the Illinois region with the cretaceous and tertiary is a distinct 

 limitation of many trees. 



