Texas Palwozoic.—Tarr. ity gi! 
in the deposition of the Trinity sands in these two places. In 
order to eliminate a possible error, even in this calculation, aris- 
ing from the complication involved by the tilting of the entire 
area in post-Cretaceous times, it may be well to take differences 
of elevation in a northeast and southwest direction, which will 
reduce the difference in elevation from 650 feet to 500 feet. The 
difference calculated here is based upon points fifty miles apart. 
That this difference is not great, when compared with the time of 
formation of the series as a whole, is proved by the fact that im- 
mediately over the Trinity, in every place, is found the lower 
layers of the Comanche Peak beds. hus it seems likely that 
the submergence of the land was tolerably rapid. This is still 
further indicated by the unassorted arrangement of the lower beds 
and their wide diversity. 
That the Carboniferous land was a level land, is proved, on 
every hand, by the fact that, on the Carboniferous proper, there 
are no excessive changes in the general level of the Trinity beds; 
but, that the Carboniferous was a land area, and one of gen- 
tly undulating surface, is equally well proved by the gradual 
changes in elevation in the different parts of the region now par- 
tially covered by Cretaceous. For instance, southwest of Brum- 
wood, on the west side of Pecan bayou, in five miles, on a north 
and south line, the elevation changes from 1,350 feet to 1,500 
feet, or an increase of 150 feet going northward five miles. The 
Santa Anna, Cretaceous butte, in Coleman county, rests in Car- 
boniferous at an_elevation of about 1,750 feet while fifteen miles 
to the northwest the Cretaceous-Carboniferous contact is at an 
elevation of 2,100 feet. At the base of the scarp along the 
Colorado river, the lowest Cretaceous boundary is a gently undu- 
lating line with a general rise to the north. The hills recently 
uncovered from beneath the Cretaceous are broad, flat-topped, and 
gently undulating. The gradual rise to the northwest is probably 
to be accounted for by the tilting of the entire mass in post- 
Cretaceous times; and it is probable that the old-land slope has 
been reversed by this means. 
From this it will be seen that there are no places where the 
position of the lower Cretaceous seems to indicate any sharp 
erosion or striking topographic relief in the Carboniferous land; 
but in the bordering Silurian the case is different. This was the 
highland of the time and, as would naturally be expected, the 
