136 Notice of Geological Surveys. 
ascent, they would lie at an elevation above low water mark of 
the Ohio, of nearly three thousand four hundred feet. 4. Grant- 
ing these me or that only a portion of the rocks were con- 
tinuous, the only authorized explanation of their absence, is a 
grand denudation by diluvial causes, which have operated in the 
general direction of this anticlinal axis of the blue limestone, and 
reduced this extensive area to one of a nearly uniform elevation. 
The immense diluvium on the Ohio, and in all the northern part 
of Indiana and Illinois; the bowlders of primitive rocks; the 
masses of native copper in Indiana ; the buried trees of Ohio, all 
indicate a mighty current from the northward, that has modified — 
most remarkably the contour of the whole country. . 
_ The history of the agencies that have operated on this conti- 
nent to give it its present face, can never be completely written 
from a comparison of the various elevations of the different parts, 
but the evidence presented by stratification, diluvium, and other 
geological resemblances, will, on the contrary, do far more to elu- 
cidate this subject, if it do not clear it up entirely. 
IL Second Annual Report of the State Graatiistet of the State of 
Michigan ; made to the Legislature; Feb. 4, 1839. 
The deficiency of maps of this state is so great that it is im- 
possible to appreciate or understand much if the topography of 
its northern and unsettled portion, and much of the minute evi- 
dence on which the geological conclusions are based, is with- — 
held for the final report. In general, the rocks of the northern 
part of the state belong to the carboniferous group, and in’ this 
respect coincide with those heretofore described as occupying the 
southern counties, — their position in the series is very dif- 
ferent.” 
“They consist of a succession of limestones, with intervening 
shales, sandstones, and clays, and at the northern extremity of 
the peninsula, the limestone is shattered in a manner similar t0 
that seen in the sandstone in the southern counties.” 
The direction of all the rocks is northeast and southwest. $a 
ginaw Bay, on Lake Huron, lies in the line of bearing, its south- 
ern shore being sandstone, and its northern limestone, both © 
which may be traced across southwesterly to lake Michigan. The 
limestone is observed at numerous points going north, at times 5° 
