CURRENT PRE-CAMBRIAN LITERATURE 843 
and porphyries to be different facies of the same magma. Further 
agreeing with Haworth, he finds that the granite occupies the lower 
ground, the porphyries the higher ground, and that, where there are 
gradations between the two, the granites are at the base of the hills 
while the porphyries are at the top, with transition zones between. 
The granites occupy a comparatively small area in the northeastern 
part of the district. This is an area of low elevation and near the 
Mississippi River, and distribution is explained as due to differential 
erosion. The physiography of the district is discussed, and the 
conclusion is reached that the crystalline rocks have undergone 
very considerable erosion since Cambrian time. Agreeing with Van 
Hise, it is held as probable that the granites and porphyries are of 
Algonkian age. A deep boring near Kansas City at a depth of 2500 
feet penetrated black foliated mica-schist, which has the characteristics 
of the Archean rocks. 
Keyes,* in connection with a description of the clay deposits of 
Missouri by Wheeler, briefly discusses their geological occurrence. 
Most of the ore-bearing conglomerates of Pilot Knob and vicinity, 
heretofore called Algonkian, are believed to be Cambrian. The 
granites and quartz-porphyries of the region are not really of Archean 
age, as generally considered, but are probably Algonkian. In chem- 
ical, mineralogical, and structural characters, and in absence of dynamic 
effects, they differ from the gneissic and schistose rocks which have 
been reached in deep drill holes, and, therefore, they are believed to 
be younger than such gneissic and schistose rocks (which, it may be 
inferred, are believed to represent the Archean). 
The geological conditions of the crystalline rocks are unfavorable 
to clay deposits. 
Comment.— No reasons are given for the belief that the ore-bear- 
ing conglomerates of Pilot Knob are Cambrian rather than Algonkian. 
Until adequate reasons are presented, the conclusion of Haworth, 
Van Hise, and other workers in the field, that the rocks are Algonkian, 
must be presumed to be correct. 
McConnell? reports on an exploration of the Finlay and Omenica 
* Clay deposits, by H. A. WHEELER — Chapter on the geological occurrence of 
clays, by C. R. KEYEs. Missouri Geol. Survey, Vol. XI, 1896, pp. 36-37. 
? Report on an exploration of the Finlay and Omenica rivers, by R. G. McCon- 
NELL. Ann. Rept. Geol. Surv. of Canada, for 1894, Vol. VII, Part C, 1896, pp. 40. 
