APPENDIX—GEOLOGICAL SURVEY. 
419 
has the same eastern and western extension. And, what is 
also very remarkable here, the Wisconsin river about ten miles 
north of it follows the course of this ridge along its whole 
length, but coming against the north and south line on the ex¬ 
treme east side of the lead district where the mineral belts 
and this ridge give out, it bends around to the north of east 
for a short distance, then turns nearly west until it reaches the 
same line, and from this place continues its course north 
through the state along the east side of this north and south 
axis. Now whether we must regard this fact, (that is the 
course of this river, now along the north side of this east and 
west elevation, and then turning at the line at which this ele¬ 
vation gives out and following along the east side of this north 
and south axis) as a coincidence, or a part of the same system 
of physical disturbance is a question for the future to decide. 
That the east and west elevation is a part of the same system 
of physical disturbance to which the lead district belongs will 
hardly admit of doubt. 
When I speak of physical disturbance, I do not mean active 
volcanic disturbance, nor active earthquake disturbance in the 
ordinary meaning of these terms, but a line along the earth’s 
crust where we have evidences of the action of mechanical 
and chemical forces that have been gently (imperceptibly it 
may be) lifting, disturbing and Assuring the rocks through vast 
periods of time, and filling those fissures with chemically de¬ 
posited material. These, rather than active volcanic forces, 
are what we usually find in connection with mineral strata. 
To these forces we shall refer again in connection with mineral 
veins. 
Commencing my examinations to the north of the lead dis¬ 
trict, along this east and west elevation, my attention was first 
directed to various basin-shaped depressions, or what are usu¬ 
ally called by the miners, sink holes. If the rocks were of 
volcanic origin I should not hesitate to call them vents; or if 
they were in the organic formation I should pass them by as chim¬ 
ney like perforations peculiar to that period; but in sandstone 
and limestones their origin is not so easily accounted for, but that 
