ANALYTICAL ABSTRACTS. 445 



the rocks have been disturbed very little from the horizontal, the average dip 

 of the strata being in a southeasterly direction at an angle probably not 

 exceeding 5 degrees. Intrusive rocks are abundantly present as sills lying 

 parallel to the stratification, resembling contemporaneous beds, and as vertical 

 dikes, some of which have been observed in continuity with the sills. Fault- 

 ing is a common occurrence in the Animikie, many scarps being due primarily 

 to this cause. 



The A rchean shares the coast line with the Animikie and Keweenian from 

 the vicinity of Port Arthur to the eastern end of Nipigon Bay, and beyond 

 this point to the outlet of the lake is the dominant series. This complex con- 

 sists of two divisions: i) a great volume of profoundly altered sedimentary 

 and volcanic rocks, characteristically schistose or in the form of massive green- 

 stones, which have suffered intense disturbance, and which correspond to 

 what has been designated the Ontarian system, and 2) immense batholites of 

 irruptive gneiss and granite, which have invaded the rocks of the Ontarian 

 system from below in the most irregular fashion, corresponding to that division 

 of the Archean which is commonly recognized as Laurentian. These Lauren- 

 tian rocks exhibit only to a very subordinate extent those evidences of dis- 

 turbances and deformation which are so abundantly apparent in the schists 

 which they have invaded. The Laurentian gneisses and granites occupy much 

 more of the shore than do the metamorphic and schistose rocks of the Ontarian. 

 Both divisions of the formation are cut by basic dikes, which, as a rule, do not 

 exceed 100 feet in width, and are vertical or nearly so. The Archean forms the 

 basement upon which the Animikie rests in glaring unconformity, the actual 

 superposition being observed at several points, with the Keweenian lying flat on 

 the latter. Very frequently, however, the Keweenian reposes directly upon 

 the Archean. 



Van Hise^ gives an historical sketch of the Lake Superior region to Cam- 

 brian time. The five divisions of this region are the Basement Complex or 

 Archean ; The Lower Huronian, Upper Huronian and Keweenawan, the last 

 three together constituting the Algonkian, and the Lake Superior Cambrian 

 Sandstone. Each of these divisions are separated by unconformities. 



The Basement Complex consists mainly of granites, gneissoid granites, and 

 of finely foliated dark colored banded gneiss or schist. The relations which 

 obtain between the two divisions are frequently those of intrusion, the granites 

 and gneissoid granites being the later igneous rocks. There is no evidence 

 that any of the dark colored schists are sedimentary, but it is certain, if a 

 massive granular structure be proof of an igneous origin, that a part of them 

 are eruptive, for between the two are gradations. 



'An Historical Sketch of the Lake Superior Region to Cambrian Time, by C. R. 

 Van Hise. In Journ. of Geol., Vol. I, No. 2, pp. 1 13-128. With geological map. 



