48 PROTOZOIC ROCKS 



the granite, or separated therefrom by chloritic or ferruginous slates, or other nieta- 

 morphic strata and decomposed beds.* These igneous rocks are coloured on the 

 map with tints of red ; lake representing the crystalline rocks, vermilion, red lead, 

 and carmine the trappean. To these formations I shall revert hereafter. 



FORMATION I. 



LOWER SANDSTONE OF THE UPPER MISSISSIPPI. 

 SECTION I. 



ITS LITHOLOGICAL CHARACTER. 



Though light-coloured quartzose sandstone constitutes by far the largest part of 

 F. 1, still the formation is not composed exclusively of that material. There are 

 intercalations of magnesian limestone, especially towards its upper part, where it 

 graduates into F. 2 ; and at certain localities argillaceous and other beds of a mixed 

 character form a considerable portion of its lower mass. 



In a practical point of view, this formation is one of importance, since it occupies 

 a large area in the District. It is not less interesting in a scientific point of view. 

 For these reasons it has received particular attention from the various corps, and 

 its members have been studied even to the elements of stratification. Some of 

 these deserve particular notice here. In enumerating them I shall follow the 

 ascending order. 



a. In the eastern part of the Chippewa Land District, the Assistant Geologist, 

 Dr. J. G. Norwood, found the lowest member of this series resting on the crystal- 

 line and metamorphic rocks, a coarse sandstone overlaid by a still coarser quartzose 

 sandstone. Dr. B. F. Shumard found an extensive quartzite formation on the Bar- 

 raboo River, extending thence south to Sauk Prairie ; he also observed a similar 

 rock associated with conglomerate, bordering the confines of the granite, in the 

 northwestern part of the District, on the St. Peter's River. In the southern part 

 of the District, on Black River, Mr. B. C. Macy found the most inferior member a 

 pebbly sandstone, with a coarse sandstone above it. On the east branch of the 

 Chippewa, Professor A. Litton observed the lowest member of F. 1 to be of a 

 similar character to that on Black River. On the main branch of the Chippewa, 

 the lowest member of the palceozoic strata which I could find adjacent to the 

 granite of the falls, is a coarse sandstone, with remarkable cross lines of deposition. 



* At the falls of the Menominie, the intrusive rocks do not seem to have reached the surface ; at least 

 our party have not detected thern. It is supposed, however, that they cannot be far beneath, for the beds 

 which usually lie in close proximity are exposed above the waters of the stream. 



