248 The American Geologist. ' ^p"^- i^^^- 
now well-known elements in Pleistocene geology, were new 
conclusions reached by the' Minnesota Survey. The existence 
and cause of lake Agassiz was stated in the first annual report. 
(5.) Owing to the divergence of the strike of the two im- 
portant iron-bearing formations in northern Minnesota it was 
observed that there were two iron horizons, thus separating 
the Mesabi range stratigraphically from the Vermilion. This 
observation was continued into Wisconsin and Michigan by a 
visit to those states, and the same duality was pointed out in 
the iron regions of those states and was announced for the 
first time in the Minnesota report for 1888. This grand dis- 
tinction having been recognized it required only the application 
of detailed field observation to complete the elucidation of the 
stratigraphy of the iron ores. The distribution of the iron ores 
of the lake Superior district has been wrought out on this 
basis. It has since been discovered that there is still a third 
iron horizon in northeastern Minnesota, not mentioning the 
titanic iron ore of the gabbro. It is the Upper Keewatin, the 
others being in the Lower Keewatin and the Taconic. 
(6.) It was the Minnesota Survey that separated the 
Archean into two non-conformable parts, viz. the Upper and 
Lower Keewatin, with a great basal conglomerate between 
them. Others had announced a basal conglomerate at the base 
of the "Huronian," but it appears that bv Huronian, in this in- 
stance, was meant the upper iron ore beds, which are not in- 
cluded in the Archean, but belong to the Taconic (Animikie). 
vSuch non-conformity also occurs in Minnesota, and is well 
known at the base of the Mesabi iron range rocks. 
(7.) It was the Minnesota Survey that detected the oldest 
known rock in the lake Superior region, and placed it at the 
bottom of the Archean. It is the greer-stoncs that were named 
Kawishiwin, the bottom rocks of the Keewatin, the supposed 
earliest crust of the globe. 
(8.) The Minnesota vSurvey also reached the conclusion 
that the great quartzyte formation which cuts quite a figure in 
the geology of Wisconsin and Minnesota is non-conformable 
upon the Animikie, and is a member of the fragmented beds 
of the Keweenawan. This has been named Sioux quartzyte, 
Barraboo quartzyte and New Ulm quartzyte. It is that which 
contains the red pipestone (catlinyte) in southwestern Min- 
