LEFT-HAND AND BLACK RIVERS. 



305 



It will be seen, from this account of the geology of Black River, that it consists, 

 like that of all this section of country south of Lake Superior and north of the 

 water-shed, of a succession of beds of marl, drift, sands and clays, red and variegated 

 sandstone, conglomerates, shales and slates, with, probably, bedded traps ; and all 

 traversed by trap dikes, — the main ones, of greenstone, having a northeasterly and 

 southwesterly bearing, and, in common with the sedimentary rocks, intersected by 

 narrow dikes of basaltic-looking trap, bearing a few degrees east and west of north 

 and south. 



All the lower members of the sandstone series found in Wisconsin and Minnesota 

 occur on this river, although no one of them is developed to the same extent that 

 they are at other localities. The sandstone does not differ in any respect from 

 that seen along the south shore of Lake Superior, between Fond du Lac and 

 Montreal River ; at the Apostle Islands ; on the waters of Bad River ; at Lake Gras ; 

 on the St. Croix, Snake, and Kettle Rivers ; and on St. Louis River, above Fond 

 du Lac Village. The lower beds are also similar in character to the red sandstones 

 found by Dr. Shumard on St. Peter's River, resting on crystalline rocks. While 

 the predominant colour is red, strata of gray, yellow, and dark brown rock are of 

 frequent occurrence ; and many of the beds are variegated with green, gray, yellow, 

 and dark-coloured bands and spots. This is also the character of some of the beds 

 on Wisconsin River, south of Whitney's Rapids. 



The upper layers decompose, almost universally, with great facility; while, 

 lower down, they become more compact and close-grained, are better cemented, and 

 would, in many places, afford a durable building rock. This is especially the case 

 in the vicinity of trap dikes. 



Except near intrusions of trap, the sandstone shows no evidence of violent dis- 

 turbance ; and in some instances the eruption of the trap has taken place without 

 any signs of the violence which is generally considered a necessary attendant on 

 such phenomena, being discoverable in beds in the near vicinity of dikes, the 

 strata remaining unbroken almost up to the intrusive rock, and the dip appearing 

 more like the result of gradual elevation, or of deposition on an inclined plane, 

 than of sudden and violent upheaval. Again, however, the sedimentary rocks 

 have been dislocated with great violence, and the broken beds lie confusedly at all 

 angles, up to a vertical position. This is especially the case where there appears 

 to have been first a series of lateral intrusions, proceeding from a main dike, 

 injected between the sedimentary strata, and afterwards the whole subjected to 

 another convulsion, sufficient to produce a complete overthrow of the intercalated 

 trappous and sedimentary beds, as seems to have been the case at the Falls of 

 Black River. 



Ripple-marks, so common in some of the beds on St. Louis River and along the 

 Lake coast in the neighbourhood of Pointe Detour, and at various other places, 

 were not noticed in the sandstones of Black River. 



The Black River conglomerate resembles in composition and colour that met 

 with near the mouth of Montreal River, and on the portage between Long Lake 

 and Alder Creek, as well as that which occurs near the mouth of Snake River, on 

 the St. Croix, above the mouth of Kettle River, between Pine Rapids and Nema- 



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