THE MONTREAL RIVER SECTION. 227 
After crossing a thickness of these beds of some 350 to 400 feet—a 
much smaller thickness than was noted farther east—a broad belt of coarse 
conglomerate is crossed. The constituent bowlders are largely of the sev- 
eral kinds of acid porphyries, but there are many of the basic igneous rocks 
of the system. Much calcite is present between the bowlders and sand 
grains, and also occurs in veins of some size. The vertical bedding is well 
brought out by the few intercalcated sandstone seams. This conglomerate 
is exposed in cliffs several hundred feet high, forming the walls of the nar- 
row tortuous gorge through which the Montreal River passes at the middle 
of Sec. 20, T. 47, R.1 E. It is plainly enough the equivalent of the outer 
sandstone and conglomerate of the Porcupine Mountains. In the latter dis- 
trict this stratum has a thickness of some 3,000 feet, but at the Montreal it 
is not more than 1,200 feet. 
Next in descending order on the Montreal is met an alternating series 
of thin and very regular beds of fine-grained diabase and red sandstone and 
shale The beds of the crystalline rocks are sharply defined from each 
other by very strongly developed amygdaloids or vesicular portions. The 
lower portions of the diabase flows are characterized by a very distinet 
columnar structure at right angles to the bedding. The finest exhibition of 
both amygdaloids and columnar structure is to be seen at the head of the 
upper falls, where at low water there is a very large surface of bare rock. 
The following tabulation, copied from my report on the Geology of the 
Eastern Lake Superior District,! serves to show the main facts with regard 
to these alternations. It should be said that detailed microscopic examina- 
tions would possibly prove some of the layers to be melaphyrs: 
Thickness in feet. 
lis JDSTRING cass bAOG) pepe U BOCOUn CORTE es AaeodieEsCOSoo.cncoorm5ooc. 20 
TI. Red shaly sandstone......-. .----+ 22sec cere ee cece eee teen eee ee es 10 
TWh. TSG 5 a2 Samat Sone Gaon edeU CHASER enone DoRtedn coonnaaa chs Ubpace 4 
IV. Sandstone and shale, including the following subdivisions: (1) thin 
laminated red shale, 4 feet; (2) purplish, lumpy, fine-grained sand- 
stone, 8 feet; (3) like (1), 24 feet; (4) like (2), 6 feet; (5) like (1), 
very bright red, 14 feet; (6) like (2), 5 feet; (7) bright red clay 
shale, 14 feet; total .... ..--..------ --- 202 cee cnet te eee etree 41 
1Geology of Wisconsin, Vol. III, p. 191. 
