1852.] OF THE ROYAL INSTITUTION. 159 
The Conglomerate is of the same age with much of the sandstone ; 
and is almost invariably placed between it and the trap. 
The conglomerates of Keweenaw and Isle Royale consist of rounded 
bowlders of trap, with a few Jaspers, cemented by red iron sand; 
but those of Memince and Nipigon contain also granites, quartzites 
and sandstones; thus indicating a difference of age. 
3. Igneous Rocks. Granite every where forms the nucleus of an 
anticlinal axis, in two parallel lines running E. and W.on the south- 
east side of the lake, flanked by metamorphic and sedimentary rocks. 
Both it and Sienite are plentiful. 
Trap Rocks. The ancient lavas of the lake are in very large 
quantities, and are well displayed. They are the great depositories 
of copper. For convenience sake, they may be divided into three 
principal forms. 
Ist. The highly crystalline mountain masses,—sometimes anti- 
clinal and sienitic. 
2nd. The bedded trap, at various angles of inclination. 
3rd. Dykes intersecting igneous and metamorphic rocks. 
They are all portions of one long series of volcanic operations. 
Trap creates the great headland of Keweenaw, with its lines of 
stair-like cliffs and hills. (It was shewn in a large diagram and 
described as typical of the trap of the whole lake.) The trap of 
Keweenaw is met with in three contiguous and parallel belts, going 
WSW., and separated by bands of conglomerate, sometimes very 
thin, often numerous, and prolonged sometimes for 40 or 50 miles. 
These three belts have been named the outer, northern, and 
southern; the last being highly crystalline, or sienitic, and abound- 
ing in chlorite. It is an anticlinal to the rocks on both sides. The 
other two belts are bedded traps, and with their interleaved conglo- 
merates dip northerly. They all coalesce at Portage Lake and after 
proceeding to Montreal River, 130 miles in the whole, soon after 
disappear under horizontal sandstone westwards. 
The north belt is the most metalliferous ; and contains the cele- 
brated Cliff and other rich mines. In the Keweenaw district it is 
the cross vein which yields the native copper —either in sheets and 
blocks or mixed in with the usual crystallizations, such as datholite, 
prehnite, stilbite, quartz, &e. 
On the Ontonagon River the metalliferous veins run with the strike. 
The copper is pure, and has interspersed through its substance, scales 
of pure silver; but without chemical union. 
The copper is confined to the trap, as an universal rule. 
The North shore of Lake Superior is eminently trappose; and 
especially about Fort William, where a region at least 120 miles long 
consists of basalt, amygdaloid, porphyries, jasper, conglomerate, and 
sandstone in the same mutual relations as on the south shore. 
