E. T. DUMBLE—VOLCANIC DUST IN TEXAU. 
33 
VOLCANIC DUST IN TEXAS. 
By E. T. Dumble. 
J Read June 14 th, 1892. 
During the field season of 1891 a number of specimens of a material 
nearly white in color and of light specific gravity were collected by 
Messrs. Kennedy and Walker from different localities in the Tertiary 
area, over which they were working. From their general appearance 
they were supposed to be diatomaceous earth, and under the micro¬ 
scope several of the specimens proved to be composed of diatoms. 
Other specimens, however, did not show any such forms at all, but 
consisted of the flat transparent, sharply angular particles with striated 
or pitted surfaces peculiar to volcanic dust, and it was so determined 
by Prof. F. W. Cragin. 
These deposits were apparently, but not certainly, all interstratified 
among the clays and sands which we have designated the Fayette beds, 
and which are probably of Miocene age. On a recent examination in 
Fayette county I found the same material under such circumstances 
as seem worthy of note, as deciding the point in that particular in¬ 
stance at least. 
The Fayette beds were described by Penrose in the First Annual 
Report of this Survey, on page 47, and in general terms may be said to 
consist of two heavy beds of sands and sandstones separated by a great 
thickness of clays and lignites. He gives the section of Second Chalk 
bluff, showing the several beds of browncoal overlaid by sands and 
clays. These underlie the upper sandstone beds of Palm bluff and La- 
Grange bluff and overlie those of Sand bluff and Muldoon. 
On the west of the Colorado river the topographic expression of 
these three series of beds is: 
For each of the two sandstones (many beds of which are indurated, 
and some even quartzitic in places) a line of detached bluffs generally 
facing north, connected by lower ridges. 
For the intervening clays and sands with browncoal, a valley eight 
miles or more in width, which is drained by Buckner’s creek and its 
tributaries. The general trend of all is about south sixty degrees west, 
from the Colorado river, and the dip of the beds is very gentle to the 
south or southeast. 
O’Quinn creek, a branch of Buckner, has its head near the base of 
the upper sandstones, and flowing northward to its junction with the 
larger stream has cut through the browncoal series, and affords, what 
is somewhat rare in this generally flat country, a satisfactory exposure 
and continuous section of the underlying beds. 
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