i8o The American Geologist. March, loos 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
The New Madrid Earthquake, by Edward M. Shepakd, Springfield, 
Missouri, (Journal of Geology, Vol. 13, pp. 45-62.) 
This paper is of unusual interest because of the explanation of 
the earthquake which is there proposed. There have been many 
theories advanced as to its cause during the century which has 
nearly elapsed since the quake, but practically all must be con- 
sidered as mere suggestions, as the writers have in general never 
visited the field nor familiarized themselves with the details of 
evidence. The fact that the problem was approached through hy- 
drologic investigations is of interest. 
Professor Shepard's explanation may be summarized as fol- 
lows: The deposits in the New Madrid region consist of super- 
ficial clayey beds underlain by fine sands saturated with water 
under considerable artesian pressure. This clay, it is thought, had 
been slowly undermined during centuries by the steady removal 
of fine sand by springs, which still exist in considerable numbers 
and bring up fine sand to the present day. A slight earthquake 
originating probably in a readjustment of some fault in the Ozarks 
communicated itself to the unconsolidated deposits, fracturing the 
clay capping, upon which the artesian pressure was relieved by 
the extrusion of the sand and water as described by nearly all 
observers, thus permitting the warping of the surface through the 
re-arrangement of the materials underlying the surface clays. A 
similar explanation is thought to be applicable to the changes near 
Shreveport, Louisiana. 
Professor Shepard's suggestion as to the origin of the shock 
in the Ozark region seems to be a good one. The wave-like undu- 
lations of the surface during the quake are characteristic of shocks 
which have been transmitted to unconsolidated materials from the 
harder rocks, and its assumed western origin is borne out to some 
extent by the fact that the shock became progressively less severe 
through the settled regions to the East. The West was not then 
settled. [1811-12.] 
The reviewer, who had the opportunity of accompanying pro- 
fessor Shepard on one of his trips into the region, agrees with him 
as to the probable point of origin of the earthquake, and as to the 
existence of a clayey surface underlain by quicksand saturated with 
water under artesian pressure. He believes, however, that the 
springs, occurring as they do only in stream beds sunk some dis- 
tance below the level of the surroimding flats, represent simply the 
normal inflow of groundwater, and are not of deep seated origin. 
Nor does the sand brought up by such springs seem to be in suf- 
ficient quantities to account for any extensive undermining. On 
