Eruptive Debris at Taylor s Falls, Minn. — Wincliell. 73 
the sandstones of the region. He had the idea that the 
igneous rock had been thrust up through the horizontal strata, 
and really did not entertain at all the later interpretation put 
upon the structure by Kloos. Mr. Kloos corrected Dr. 
Owen's explanation, showing conclusively that the sandstone 
was deposited upon the igneous rock as a debris of erosion 
after the igneous rock had cooled, and that at the bottom of 
the sandstone was a conglomerate composed almost entireh 
of pieces of the igneous rock. This view has been adopted 
by all subsequent observers. Irving often quoted this local- 
ity to show that the Keweenawan formation is unconformable 
beneath the horizontal sandstones and that a profound erosion 
interval separates the two formations. 
At a meeting of the University Geological club, about a 
year ago, this conglomerate was incidentally under discussion 
in connection with a paper read by Mr. Berkey. From gen- 
eral taxonomic studies of the Keweenawan and its relations 
to the sandstones, published in 1895, the writer was strongly 
impressed with the probability that at Taylor's Falls were 
various interesting facts yet undeveloped by foi"mer observa- 
tions, one of which would probably be the separation of the 
conglomerate into two congloiiierates, each being at the bot- 
tom of one of the parts into which the Cambrian in the north- 
west is divisible, and the lower one separating the eruptives of 
the Keweenawan (as described by Irving), into two parts. 
Since that, several important and interesting discoveries 
have been made, as follows, in the order in which they were 
brought out: 
1. The first important fact is due to microscopical exam- 
ination, viz: in some thin sections examined by Mr. Berkey, 
the rock from which they are derived is found to be a tufT 
or grit of eruptive materials. The parts are sub-angular and 
rounded, consist very largely of a highly doubly refracting 
mineral like epidote, of devitrified glass and of quartz. It is 
evident therefore that if this rock resulted from volcanic activ- 
ity at the time of its formation, the fragments were wholly 
wrought over by some detrital action. 
2. On visiting the place in company with Mr. Berkey he 
guided me to the spot at which this rock appears. It is at 
the corner of Government and West streets, about 200 feet 
