328 PROCEEDINGS OF THE ACADEMY OF [1893. 



Hill ascribes their presence here to the influence of the sand 

 which, by its porous nature and the fact that it is a storehouse for 

 moisture, renders tree growth possible, whereas the clays of the prai- 

 rie are too close grained for forest growth. I find myself unable to 

 agree with Prof. Hill on this point, for I believe the cause of 

 the absence of forested areas on these plains is to be found in the 

 habit which the Indians had of setting fire to the prairies in order to 

 facilitate the search for game. 24 My reason for the belief is that 

 wherever in this region, for any reason, the growth of grass is sparse, 

 forests or groves or scattered trees grow. In the Carboniferous 

 area, enclosed in part in this Grand Prairie, the hill sides are 

 almost invariably covered with a sparse tree growth, whereas the 

 low undulating divides are treeless, although there is very little if 

 any difference in character of soil, except that the hill sides are 

 more rocky. This is true on both limestone and sandstone soils. It 

 seems to me much more reasonable to suppose that, being sandy, 

 these areas supported a growth of vegetation too sparse to readily 

 spread the prairie fires and were consequently protected from them 

 and therefore are forested. From my view of the Cross Timbers in 

 a drive across them I feel confident that a fire could not long burn 

 in them, for they are low scrub oaks and very much scattered. 



(c) Rejuvenated Peneplain. — The drainage of the Cretaceous pla- 

 teau is young, or, more properly, rejuvenated. There are great 

 areas of Cretaceous removed, so much indeed that I think it 

 extremely unlikely that it has all been removed in the present cycle. 

 The stripping of the covering from the central Palaeozoic prairie, 

 the removal of the upper Cretaceous beds from the Grand Prairie, 

 and the uncovering of the Shumard Knobs and their subsequent 

 denudation are hardly in keeping with the supposition that this 

 work has been done by young streams. My acquaintance with the 

 drainage of the Cretaceous Grand Prairie is so slight (being confined 

 to the vicinity of Austin with the exception of one or two trips 

 across it on the railroad) that I cannot state as a definite fact the 

 history of the region which I suspect ; but there is a line of reason- 

 ing which renders it highly probable that before the Tertiary eleva- 

 tion the Cretaceous was reduced nearly to sea level. It is as follows: — 

 In the first place the vast denudation mentioned above suggests 

 long continued erosion. At the beginning the Cretaceous was at 

 least seven hundred feet lower than at present, and this condition 



"Shaler— Aspects of the Earth,— New York, 1889, p. 287- 



