Geology of the Lake Superior Land District. 23 
solidated beneath the pressure of a deep ocean, while from the 
former a greater part of this pressure may have been removed ; 
or it may be that both were, in the first aaeenia equally 
vesicular, but that the latter assumed a crystalline or compact 
structure from long-continued ae ‘8 heat, under immense 
pressure. All the “phe nomena wou m to indicate that the 
a of the trappean rocks of this siete took place beneath 
an ocean of great depth; or, at least, under conditions widely 
diteisne from those which prevailed during the formation of the 
trappean belts of Keweenaw Point and Isle Royale. 
Remarks.—The investigations of geologists in different parts of 
the world, within the last few years, have clearly demonstrated the 
existance of a series of non-fossiliferous rocks below the Silurian or 
Cambrian systems, and there can be no doubt that they are des- 
tined to occupy a conspicuous place in the classification of the 
rocks both of Europe and America. At the meeting of the 
American Association at Cincinnati, in the spring of 1851, we 
made the development of this system in the northern portion of 
the United States and Canada the special subject of a communi- 
cation. Professor Mather, after having confirmed the pepe 
of our views, from personal observation, stated that ad ob- 
served the continuation of this system near the sources of the 
Mississippi, and on the waters of the St. Peter’s. Its existence 
in Missouri, where it is associated, as on Lake Superior, with 
immense beds of magnetic, and specular i iron ore, is rendered cer- 
tain by the observations of Mr. Mersh, which will be found 
incorporated in the paveeatieet, ‘ages of this report. At this 
meeting, Dr. King, who has examined this region with much 
care, confirmed these views, eg we regret that the proceedings 
have ‘i yet been made public, that we : might quote his remarks 
in full 
Dr. Engelman, also, on that occasion, described a series of azoic 
rocks, as occurring in Arkansas, between Little Rock and the 
Hot Springs, which present a striking analogy with those of 
Missouri and Lake Superior, consisting of talcose, silicious and 
crystalline hornblende slates, often highly inclined, with beds of 
dark-blue limestone. On these older rocks, rests unconformably 
a sandstone, probably analogous to that o e Superior, 
Within this district of non-fossiliferous, stratified rocks, occurs a 
beautiful syenite. The vast masses s of micaceous, or ‘sul-m ag- 
hetic oxyd of iron, which occur in Missouri, find their represent- 
ative in the well known “ Arkansas Magnets, ”? or, in the iron ore 
of Magnet Cove. It is here associated with the imesseves 
titaniferous minerals, schorlomite, brookite, and elzolite. Dr. 
thinks he has traced this series on the northern oie of the 
Colorado in Texas. 
