90 GUIDEBOOK OF THE WESTERN UNITED STATES 
Beyond the edge of the gravel plain 5 miles west of Tesnus thin- 
bedded sandstone and shale of the Haymond formation are exposed 
in some of the railroad cuts, and the massive arkose, which directly 
underlies the boulder bed, crops out in conspicuous ledges along the 
edge of the valley not far to the south. After crossing the Haymond 
beds the railroad follows the gap cut by San Francisco Creek across 
the sharp, narrow ridge of steeply tilted Dimple limestone, a ridge 
typical of the outcrops of this formation throughout the Marathon 
Basin, and continues down the valley past Haymond, which is on 
an anticlinal area of Tesnus sandstone, some ledges of which are well 
exposed along the railroad and creek. 
Haymond siding, which lies in the valley of San Francisco Creek, 
is now a very small place but was at one time a town of considerable 
size. It was the railroad station for Fort Stockton, 
epee rs: 60 miles to the north, when that was an important 
een oe oi: Sreuaer fort The rocky hills near Haymond are 
underlain by various formations of Pennsylvanian 
age. To the east and west of it are low ridges of the Dimple limestone, 
between which are lower lands underlain by sandstones and shales of 
the Tesnus and Haymond formations. These rocks are folded into 
several sharp anticlines and synclines. 
Northwest of the ridges of Dimple limestone the railroad again 
enters a much gullied plain of terrace gravel, underlain by sandstones 
and shales of the Tesnus formation. The Caballos novaculite (Devo- 
nian?), which lies beneath the Tesnus, crops out to the northwest, 
about 3 miles beyond Haymond, in low ledges and ridges. This 
novaculite is a white siliceous rock, probably a variety of chert, in 
more or less massive-bedded layers. The name was applied to closely 
similar “‘whetstone rock” in Arkansas by Schoolcraft in 1819. Novac- 
ulite is of rare occurrence in this count 
sedimentary rocks as sandstone, shale, and limestone. 
,in comparison to such other 
The novacu- 
rounded and angular masses of rocks 
of many kinds, most of which do not 
crop out in the Marathon area. The- 
fragments are rather widely set in a 
a of arkosic mud and consist of 
Camhri 
, gran ite, 
schist, aplite, and pegmatite. 
, an 
ceous breccia, probably a fault breccia. 
Blocks 5 to 15 feet across are common, 
and one block of Dimple limestone 
south of the railroad is over 100 feet 
long. The large masses, however, are 
most abundant a mile or more north of 
the railroad. 
The various pre-Cambrian to Car- 
boniferous ingredients in this conglom- 
erate indicate that there was a near-by 
area of upturned older strata in upper 
Haymond time. Probably it was situ- 
ated south of the present uplift and is 
now deeply buried beneath younger 
strata. It is difficult to understand 
how the coarse materials were trans- 
ported to their present position, for the 
larger masses could not have been car- 
ried by streams; they may 
have been overthrust—a condition that 
might account for the presence of the 
blocks of fault breccia. 
