392 
Tne American Geologist. 
June, 1896 
which is post-Tertiary and in age immediately precedes the present pe¬ 
riod of stream cutting. 
It is of interest to examine this area, as forming a portion of the 
Ozark uplift, in connection with Russell’s recently published notes upon 
‘"The Nature of Igneous Intrusions.* The similarity existing between 
the structure of the Black hills and the Ozarks is striking. In each the 
central core is a mass of granite surrounded by sedimentaries which dip 
steeply away from the crystalline core, but within a short distance be¬ 
come horizontal. Russell would regard the Black hills as due to an in¬ 
trusion of molten rock which took place below the surface and which 
on account of the weight to be lifted and the viscosity of the mass 
did not expand into a sheet, but produced local elevation. The expo¬ 
sure of the core of the hills is due'to a period of later erosion. 
That the original shape of the Ozark uplift was such a dome has been 
inferred by Winslow and others, and that the amount of erosion since 
has been very great may be inferred from the remnants of Coal Measure 
strata and the superimposed streams, as well as the great differences in 
elevation between the Tertiary peneplain and the Farmington lowland 
described by Keyes. The character of the igneous rocks is also similar 
to that of those found in the Black hills and the legitimate inference 
would seem to be that in origin the two uplifts were similar. There 
must, however, have been in the Ozark region considerable differences 
in elevation before the sedimentary beds were deposited, as is shown by 
the marked unconformity between the two and the presence of a basal 
conglomerate. Indeed Keyes says: “The marked inclination of strata 
which has often been ascribed to low folds is the result of peculiarities 
in the original deposition of the beds, and not of deformation after sed¬ 
imentation had ceased. Very noticeable dips are apparent where the 
stratified rocks rest upon the ancient crystalline hills,” — p. 57. The 
presence of a similar unconformity below the “Potsdam” of the Black 
hills, as noted by Newton, would seem to indicate similar conditions 
and would apparently lend support to the belief that in each case the 
uplift is due to the intrusion of a laccolitic mass below the granite. 
H. F. B. 
Mineralogie de la France et de ses Colonies : Description physique et 
chimique des mineraux , etude des conditions geologique de leurs gise- 
ments. Tome premier. Par A. Lacroix. (Baudry et Cie, 1893-1895, 
Paris. ) This volume has been published in two fascicules, the first hav¬ 
ing appeared in January, 1893. The appearance of the second fascicule, 
completing volume 1 of the work, occurred in December, 1895. This 
volume contains 719 royal octavo pages and has numerous figures 
throughout illustrative of the crystallographic and optical characters of 
the minerals discussed. The classification adopted is that of Groth, 
but modified by the introduction of the basic silicates and the titanates 
in the first part of this volume. The second volume, now in press, will 
be devoted to the feldspars, carbonates, sulphides, etc. 
*Jour. Geol., iv, 2, pp. 175-194, 1896. 
