CURRENT PRE-CAMBRIAN LITERATUKE 841 
the contrary is produced, but that there now exist certain doubts con- 
cerning the accuracy of this view. 
Keyes,’ in an account of the characteristics of the Ozark Moun- 
tains, briefly describes the Archean and Algonkian rocks of the region. 
Archean rocks occur at the east and west ends of the Ozark uplift. 
The best known of the areas is the eastern one, the Iron Mountain 
district of southeastern Missouri. Here the largest areas occur in the 
vicinity of the peak from which the district takes its name, and other 
smnaller areas are scattered over a considerable range of adjacent terri- 
tory. The Archean rocks in the Iron Mountain district are granites 
and porphyries, the latter predominating, both of which are broken 
through in numerous places by basic intrusives. 
At the western end of the Ozark uplift, in Indian Territory, are 
Archean rocks, principally granites, of which there are many varieties, 
cut, as in southeastern Missouri, by dikes of basic material. 
Immediately overlying the Archean in a number of places are beds 
of conglomerates and slates provisionally referred to the Algonkian. 
These appear to best advantage on Pilot Knob. 
Haworth? describes and maps the pre-Cambrian geology of the 
area of the Iron Mountain sheet in southeastern Missouri, which covers 
portions of Iron, St. Francois, and Madison counties. The pre-Cam- 
brian rocks are crystalline, massive, Archean rocks, and crystalline, 
stratified, Algonkian rocks. 
The Archean rocks in general form the uplands. They may be 
divided into two general classes, basic eruptives and acid eruptives, 
including granites and porphyries. 
The basic eruptives, of remarkably uniform character, occur prin- 
cipally in the southeastern part of the area, usually in dikes cutting 
through the granites and porphyries, but in a few cases in the form of 
bosses almost circular in outline. The general trend of the dikes is 
northeast-southwest. 
The granites occur mainly in two large areas, though they are 
found occasionally in small patches within the porphyries. The two 
1 Characteristics of the Ozark Mountains, by C. R. Kryrs. Rept. Missouri Geol. 
Survey, Vol. VIII, for 1894, pp. 317-352. 1895. 
2Report on the Iron Mountain sheet—the Archean rocks, by ERAsmMus 
HawortH. Rept. Missouri Geol. Survey, Vol. IX, 1896, pp. 15-27. With Sheet 
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