Origin of the Menard "Crater"
by Emmett Blakemore
On August 30, 1938, the
foreman of the Wilkerson
Ranch twelve miles southwest
of Menard, Texas, reported
that a meteorite fell
on the ranch and created a
large crater. The story,
widely publicized by newspapers,
caused the writer,
accompanied by Professor
J. D. Boon of Southern
Methodist University, to in- Fig. 1. Location of Menard sink.
vestigate this phenomenon. The reported crater was found
by following the Menard-Ft. McKavett highway west nine
8 FIELD AND LABORATORY
miles from Menard to the intersection of a cross-road,
thence north three miles to a point 100 yards east of the
"crater". Approximate location is shown on map (Fig. 1).
Fig. 2. The j\1(cnard sink, reported erroneously as a mereor i[c Crater.
The hole reported to be a meteorite crater was found
to be roughly circular in plan with a diameter approximately
twenty-five feet and a depth of about thirty feet (Fig. 2) .
The bedrock of the region is one of the limestone beds of
the Fredericksburg group. About five miles south, the San
Saba River has eroded through the Fredericksburg and
developed its valley on the Trinity group. In the walls of
the pit a cobble conglomerate is exposed, the cobbles being
fragments of the Fredericksburg limestone with an impure
limy matrix which gives poor cementation. This
conglomerate resembles very closely the piles of gravel in
the bed of the nearby San Saba River. Similar conglomerates
with interbedded silt and clay fill numerous abandoned
stream channels exposed in road cuts in the area. The
distinct horizontal bedding in the conglomerate is best
shown near the edge of the pit, where the rock contains
less water. Apparently the bottom of the hole is composed
of the same material as the enclosing walls except that the
MENARD CRATER
south side is covered by slumped soil containing traces of
grass. The depth of the bedrock at this point, could not
be determined.
It is difficult to see any relationship between this pit
and craters known to be of meteoritic origin. There is no
rim of ejected material. There is no evidence of distortion
in the beds exposed at the brink; grasses grow to the
margin, and at one place a mesquite tree hangs precariously
over the hole with its roots dangling. The mesquites
growing close to the pit and the one which hangs partially
over it show no signs of the intense heat which would be
associated with a falling meteorite.! The cobbles in the
bottom of the pit are unfractured, as are those of the conglomerate
composing the walls. Some fracturing and pulverization
would be expected should a meteoritic origin be
assumed. A magnet used in the area did not gather iron
fragments.
The Menard crater is a limestone sink. It is situated
in a region of soluble limestones and marls in which numerous
caverns have been excavated. The month preceding
the formation of the sink was one of heavy rains and
floods; subsurface erosion should have been at a maximum.
All of the material which once filled the hole appears to
have moved downward to fill a collapsed cavern.
This pit is neither unusual nor fundamentally different
from the innumerable sinks that dot the Edwards
Plateau. This paper is designed to correct a popular fallacy
regarding the origin of the Menard "crater", one
which might cause future investigators of meteorite craters
unnecessary travel and expense.
'Rogers, A. F., (1930) "A Unique Occur,nce of Lech,l elier;le or Silica Glass",
American /ollrnlll of Science, 51h Series, Vol. XIX, pp. 195 -202 .
reprinted from- See two photo images of the "crater"-
https://sites.smu.edu/shulermuseum/publication_pdfs/field_lab/Blakemore1939a.pdf
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