176 The American Geologist. Mareh, 1892" 
shore line deposits of local origin.” If these beds are Trinity or 
lower Comanche limestones it merely proves that at this time the 
older rocks were not completely submerged; but if they belong to 
the higher beds the argument is quite unanswerable. ' 
Thirdly. The irregularity in dip of the Cretaceous is men- 
tioned. This is not the case in the more northern region which | 
have studied. This irregularity in dip may have been due to 
original irregularities of the old land surface or to subsequent 
deformations which Dr. Comstock himself has proved to have 
oecurred in the region under consideration. | 
The fourth and fifth arguments refer to the etfects of faults in 
the older rocks, the meaning of which I cannot quite make out 
from the brief statement which he was obliged to make. Having 
no knowledge of the region in question or the phenomena referred 
to, I should not feel myself qualified to answer these arguments. 
The sixth argument is the vast erosion shown in the older 
rocks, far too great to have been accomplished in post-Cretaceous 
times. This is precisely the ground that [ have taken above in 
attempting to show that the central core has been subjected to de- 
nudation from before Carboniferous times to the beginning of the 
Cretaceous 
Dr. Comstock’s seventh argument is that the pre-Cretaceous 
topography is still being perfected, the present streams occupying 
the old valleys, quite in contrast to that which is seen in the 
area only recently uncovered from beneath the Cretaceous. A 
stream superimposed upon a lower rock through an unconform- 
able covering finds itself following an irregular course, with little 
regard to revealed topography and structure. It is now pretty 
well proved that the streams will eventually adjust themselves 
to the newly formed topography. I have attempted to show, in 
articles in the American Journal of Nevence, that this has been the 
case in the Carboniferous area of central Texas. Where recently 
uncovered the streams flow over the Carboniferous in very irregu- 
lar courses, but, as you proceed away from such places, they are 
found more and more in conformity with the Carboniferous struc- 
ture. ‘The tributaries to the Colorado, and that river itself, show 
such adjustments. In a region like the older Palaeozoic which is. 
so much more diversified in topography and structure, so much 
more elevated and, probably, so much longer uncovered, this pro- 
cess of adjustment has had both more time and opportunity for 
