walcott.] SUMMARY — LAKE SUPERIOR SANDSTONE. 337 



very irregular seams, from a fraction of an inch to several inches thick. Some of the 

 round clay patches appear as if formed by the decomposition of granite or gneiss 

 bowlders imbedded in the sandstone at the time of its formation. 1 



In speaking of these same sandstones Mr. E. T. Sweet says : 



In regard to the age of the Lake Superior sandstones, but very little in deed can be 

 learned in the western Lake Superior district. So far as my observations have ex- 

 tended, the sandstones are absolutely devoid of organic remains. They are removed 

 many miles and are separated by intervening older formations from the unmistak- 

 able Lower Silurian strata. 



He considers it has been conclusively shown that the sandstones are 

 of more recent age than the Keweenawan strata. 2 



Dr. C. Eominger concluded from his studies of the Lake Superior 

 sandstone that its Lower Silurian age was unequivocaHy proved by its 

 stratigraphic position. In its whole extent it is visibly overlaid by cal- 

 careous ledges containing fossils peculiar to the Calciferous formation, 

 or, in other cases, by the Trenton limestone. He describes the sand- 

 stone east of the Copper Range of the Keweenaw Point and divides it 

 into two sections, an upper and a lower one. He says : 



The upper section is composed of light-colored, almost white, sandstones of generally 

 soft, friable nature. The lower section is intensely red colored by iron pigment, and 

 contains various hard, compact ledges, which are valuable building stones. West of 

 Marquette only the lower section of the group is developed; east of it the heights 

 are formed by the upper division; the lower has exclusive possession of the shore as 

 far as Grand Island Bay. East of Grand Island Bay the upper division sinks down 

 to the level of the water, and only in limited spots the lower red-colored strata come 

 to the surface. 3 



On Laughing Whitefish Eiver a section as determined by Dr. Kom- 

 inger is as follows in ascending order : 



m Feet. 

 No. 1.— Alternations of thin-bedded, hard, often micaceous sandstone slabs, 



with arenaceous shales (as exposed) 25 



No. 2. — A iine-grained, more or less argillaceous red sandstone in layers of 



1 to 3 feet in thickness with seams of red shales 12 



No. 3. — A hard, coarser-grained, red, or speckled sandstone in heavy ledges up 

 to 4 and 5 feet in thickness, amounting in the aggregate to 15 or 20 

 feet 15-20 



No. 4. — Light-colored, middling soft sandstone in thick layers with seams of 

 quartz pebbles, followed by a few feet of a dark and coarse conglom- 

 erate ; thickness not accurately ascertained 00 



No. 5. — A series of thin-bedded, soft, whitish sandstones, each layer separated 



from the other by a narrow seam of bluish shale 75-100 



'No. 6. — Massive soft white sandrock, projecting in vertical walls 50 



Directly above this, strata of the Calciferous sandrock occur with 

 casts of rieurotomaria. 4 



This section of Dr. Kominger's is not altogether complete, but it shows 

 conclusively that the Lake Superior sandstone in the vicinity of Mar- 



1 Lake Superior sandstone [Geology of the Western Lake Superior district]. Geology of Wisconsin, 

 Survey of 1873-'79, vol. 3, 1880, pp. 208, 209. 

 *Op. ci*., pp. 351,352. 



'Paleozoic Rocks. Geol. Survey Michigan, Upper Peninsula, 1809-1873, vol. 1, pt. 3, 1873, pp. 80-82. 

 *Op.cit.,pp.88-90. 



Bull. 81 22 



