750 PRE-CAMBRIAN NORTH AMERICAN LITERA TURE 



jasper and these iron-bearing slates are the equivalents of the iron- 

 bearing formation and the quartzite below in the Marquette district. 

 If the latter proves true the principal ore horizon of the Menominee 

 may have an equivalent in the Marquette district. 



Weidman' describes the igneous rocks of the Lower Narrows of the 

 Baraboo River. These are in a belt from one-eighth to one-half mile 

 wide, running for four miles in a direction east and west. Chemical 

 and microscopical study shows this rock to be a quartz-keratophyre. 

 It is shown to be a volcanic rock by its flowage structure, broken crys- 

 tals, and by volcanic breccias. The rock has a schistosity parallel to 

 the bedding of the quartzite. The quartz-keratophyre rests upon the 

 topmost layer of quartzite, with a possible erosion interval. It has 

 been folded with the quartzite, and like that rock rests unconformably 

 below the undisturbed Cambrian. 



Beyer^ describes spotted slates associated with the Sioux quartzite 

 series in the northeast corner of Minnehaha county. South Dakota. 

 The quartzite here grades up into reddish slate, which in lithological 

 character corresponds to the quartz-slate described by Irving and Van 

 Hise in the Penokee series of Michigan and Wisconsin. 



Bayley ^ gives fully 'the f:eld occurrences, relations, and petrography 

 of the eruptive and sedimentary rocks of Pigeon Point. The oldest 

 rocks are interbedded Animikie slates and quartzites. Cutting the 

 Animikie rocks is an olivine-gabbro, which occupies all the higher 

 portions of the point. It is in all probability the lower portion of a 

 large dike, whose upper part has been removed by denudation. 

 Between the gabbro and the bedded rocks in many places are suc- 

 cessively a coarse-grained red rock, a fine-grained red rock (quartz- 

 keratophyre) and a series of contact rocks. The main masses of the 

 keratophyre occupy a position between the Animikie sedimentaries 



^ On the Quartz Keratophyre and Associated Rocks of the North Range of the 

 Baraboo Bluffs, by Samuel Weidman. Bull. Univ. of Wis., Sci. Ser., Vol. I, 1895, 

 PP- 35-56, pis. 1-3. 



= The Spotted Slates Associated with the Sioux Quartzite. by S. W. Beyer 

 lohns Hopkins Univ. Circulars, No. 121, 1895, P- 10. 



3 The Eruptive and Sedimentary Rocks on Pigeon Point, Minn., and their con- 

 tact phenomena, by W. S. Bayley. Bull. 109, U. S. G. S., with maps and plates. 

 Washington, 1893. 



