THE GEOLOGICAL SECTION OF MICHIGAN 691 
Keweenaw Point, but to the Nonesuch shale on Black River it must 
be much thicker, not allowing for initial dip at least 3,500 feet. 
Irving estimates 3,000 feet in the Porcupines. 
8. Nonesuch formation (from the Nonesuch mine).—Dark colored 
shales and sandstones—owing its dark color to the basic material—a 
very significant sign of heavy erosion of Keweenawan traps at some 
distance. This seems to be a very persistent horizon in lithological 
character, in spite of not being very thick, being 600 feet on the 
Porcupines, 500 feet on Black River, and 350-400 on the Montreal. 
g. “Freda sandstone.” ‘Main body of sandstone” or “western 
sandstone”’ of Rominger (not Irving). This seems to need a local 
name and may well take it from the new stamp-mill town on the 
shore of Lake Superior, not far from Portage Lake Canal, near 
which exposures occur, and a well showed a thickness of over 970 
feet of sandstones and shales. The relation of this to the ‘‘Lake 
Superior sandstone”’ in general is a mooted question. It was included 
in it by early writers. It is much like it lithologically and struc- 
turally though felsitic and basic débris and streaks of red clay may be 
rather more common and the water more saline than in the Lake 
Superior sandstone around Marquette. The one mantles a granitic 
boss from which the other was separated, as the Nonesuch shale 
shows, by extensive exposures of Lower Keweenawan. 
Wells in unquestioned Lake Superior sandstone at Lake Linden 
and Grand Marais show that it is 1,500 feet and over thick. The 
dips are generally less than those of deposition, so that we cannot 
make much use of them. Irving estimates the thickness at 12,000 
feet, but this is, we believe, based solely on the questionable Montreal 
river section. We do not, however, think, that it will be decreased 
below 4,000 feet, if we allow 1,500 feet to the Lake Superior sand- 
stone and make 8,000 feet for the whole upper Keweenawan. We 
repeat that we are not at all sure that there is any other than an 
arbitrary dividing line between it and the sandstone which we propose 
to call Jacobsville. 
Lake Superior sandstone.—This term was used by Houghton, and 
has been customary since, the term Sault Ste Marie sandstone being 
much later and less used. It is often and quite properly called the 
Potsdam. It is necessary only to refer to the supposed equivalence 
