THE SOUTH RANGE. 201 
descent, the base of the Upper Division lying not more than half a mile 
inland at the latter point. 
The total thickness of the Keweenaw Series between the Eastern Sand- 
stone and the lake coast on the line of the Ontonagon River is some 28,000 
feet, of which about 12,500 feet belong to the Upper Division and the re- 
mainder to the Lower Division. This estimate is based upon the breadth of 
country occupied, and the trends and dips of the strata. The Lower Divis- 
ion, constituting the Trap Range, occupies much the narrower belt, on ac- 
count of the higher northern dip of its beds, while the Upper Division has 
a broad spread, on account of the flat dips of the sandstones composing it, 
this dip lessening rapidly as the Trap Range is receded from, until at the 
lake it varies only a very few degrees from horizontality. The greater 
thickness of the Upper Division present in the Ontonagon as compared with 
the Portage Lake section is of course due to the rising of the coast west- 
ward in geological horizon, and not to any actual increase or decrease in 
thickness. 
SEcTion III.—THE SOUTH RANGE. 
The low area lying south of the Keweenaw Point, or Main Trap 
Range, and underlain by horizontal sandstone, extends from Béte Grise Bay 
for over a hundred miles in a southwesterly and westerly direction, as far 
as the western part of T. 48, R. 44 W., west of Lake Agogebic. Keweenaw 
Bay occupies much of the eastern part of this depression, everywhere south 
of which is again a belt of high country. This southern margin, in the 
vicinity of Keweenaw Bay, is composed of the iron-bearing schists gen- 
erally referred to the Huronian system. Farther west, however, these 
iron-bearing schists have between them and the horizontal sandstone on 
the north a belt of rocks closely similar to those of the Main Range, forming 
the northern border of the sandstone-filled depression; 7. e., they are bedded 
diabases and amygdaloids, including porphyry-conglomerates. This is the 
belt to which the name of South Trap Range was given by early ex- 
plorers.* 
1 The information obtainable with regard to the South Range was very scanty previous to the be- 
ginning of the special work on which the report is based. 
