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. é 
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- 
39 
