ALGONKIAIST EOCKS OF STUEGEON EIVER TOKGUE. 473 



beds in the dolomite series. If these represent the upper portion of the 

 dolomite formation, as is the case with similar rocks in the Felch Mountain 

 range, it is clear that as we approach the center of the Sturgeon River 

 tongue the rock beds met with are j^ounger than those on its borders'. This 

 is in line with the supposition that the Sturgeon River tongue is a westward- 

 pitching syncline. 



The belief that the conglomerates are beneath the dolomites in the 

 Sturgeon River area is further strengthened by the fact that the principal 

 conglomerate in the Felch Mountain range is beneath a dolomite which is 

 identical in character with the Sturgeon River dolomite. This conglomerate 

 is regarded as the base of the Lower Menominee series in this district, with 

 the dolomite above it, known as the Randville dolomite, immediately suc- 

 ceeding it. If the conglomerates and dolomites in the two districts are the 

 same, the Sturgeon River rocks are Lower Menominee. 



RELATIONS BETWEEN THE DOLOMITES AND CONGLOMERATES AND THE 

 OVERLYING SANDSTONES. 



At several places the conglomerates and dolomites are overlain bj 

 well-defined Lake Superior sandstone. The sandstone usually ca^js hills, 

 on the lower slopes of which ledges of the undei'lying rocks appear. The 

 contacts between the overlying sandstone and the underlying rocks are 

 rarely seen, but the fact that the former are always horizontal, while the 

 latter are always very steeply inclined, leaves no doubt that there is a 

 strong unconformity between them. 



THE CONGLOMERATE FORMATION. 



The conglomerate formation comprises very much squeezed granitic 

 conglomerates, arkoses, sericite-schists, quartzites, a few beds of banded 

 rocks believed to consist largely of tuifaceous material (see pjD. 486-487), 

 and occasional beds of slates. Nearly all the members of the series are 

 schistose, the arkoses in some cases passing into very well characterized 

 sericite-schists. Occasionally the arkoses show obscure traces of ripple 

 marking, and more frequently very well defined cross bedding. 



All the rocks of this formation strike in a nearly uniform direction, N. 

 75°-84° E., and dip almost vertically. In one or two instances observed 

 the dip is as low as 65°, but in most cases it varies between 85° N. and 

 85° S. The strike of the sehistosity is approximately parallel to the strike 



