Texas Palwozoic.— Tarr. 173 
The pebbles are frequently well rounded, and are sometimes, as 
for instance, south of Milburn, fully one and one-half feet in 
diameter. They are almost exclusively of flint and marble from 
the Silurian. 
Iam not able to account satisfactorily for such a conglomerate. 
At first I was inclined to the belief that it represented old river 
beds, and I am not certain that this will not be found to be the 
origin of some of these conglomerates. The rather linear ar- 
rangement, in places, the fact that many miles away from the 
Silurian large pebbles from this source are found, and the presence 
of silicified wood and land fossils seem to indicate this origin. 
The close resemblance which some of this conglomerate bears to 
quaternary conglomerates in the creek beds is very striking. 
In Wallace creek, west of San Saba, the pebbles brought from 
the Silurian in times of flood, are cemented by a tufaceous ma- 
trix, deposited from chemical solution by the evaporation of the 
water, and this conglomerate resembles the Cretaceous so closely 
that several good observers have at first sight considered hand 
specimens of the two the same. 
Certainly this is not an ordinary beach conglomerate, for, in 
addition to being composed of large and sometimes well rounded 
pebbles, it is composed, in fully one-half its bulk, of a matrix 
of limy matter. We have a basis for comparison in the same 
field, for, near Rochelle, Cretaceous conglomerate rests directly on 
the Carboniferous conglomerate. Not only is there no resemblance 
between the two in the character of the matrix, but the pebbles 
also, though derived from the same source in both cases, are en- 
tirely different, The Carboniferous conglomerate has no pebbles 
of marble, but the Cretaceous contains very many marble pebbles 
in addition to the flint derived from the marble. This compari- 
son shows that, while the Carboniferous conglomerate had been 
subjected to much sea-shore grinding, the Cretaceous was almost 
free from such action. 
It can be readily shown by subtracting the present slope of the 
old Carboniferous land from the dip of the Cretaceous that the 
dip of the old pre-Cretaceous land was several feet per mile to 
the northwest. Consequently as the land sunk beneath the sea 
the water encroached from the west toward the east. 
The Trinity beds are probably nothing more than hurriedly 
worked over soils and land debris, in a rapidly encroaching sea, 
