APPENDIX—GEOLOGICAL SURVEY. 
453 
such beds of rock would necessarily present itself to us in a 
variety of forms. It might pass through friable sandstone 
without leaving the sign of a fissure, while the same force 
opposed by the cohesion of the limestone would become an 
elevating force, gently lifting the thin beds of rock (in some 
places passing between them) while seeking to force a passage 
through. In this way, the fissures along a line of phyical dis¬ 
turbance would vary in form and character in proportion to 
the nature and degree of resistance opposed to the mechanical 
force in its passage through the different beds. 
Another result of mechanical force acting upon such strata 
through a fluid medium, especially if it should be rising from 
fissures in a lower and older formation, would be as follows: 
Coming in contact with a bed of friable sandstone, this fluid 
medium (whether water or vapor) would be scattered through 
a large portion of the rock, reaching the beds of limestone 
above in a different condition. In such cases, instead of a 
single fissure over the centre of force, we should find groups 
of fissures scattered over a wide surface. Such phenomena 
are common in mineral strata. 
Mechanical forces also differ in their character and mode of 
operation ; consequently fissures that are produced by them are 
different. Hence to obtain a correct knowledge ol the differ¬ 
ent forms and systems of fissures it is important that we study 
these forces and their results in their separate forms. An il¬ 
lustration, perhaps, will place this subject in clearer light 
than any language that I can command. 
Suppose the Blue Mounds, the Platte Mounds, Sinsinnewa 
Mounds and other elevations of land in the lead district were 
elevations of granite or any other plutonic rocks, that were el¬ 
evated subsequent to the formation of the strata of that dis¬ 
trict; the result would be extensive displacement of the prior 
formed rocks; it could not be otherwise. Another result 
would be, the rocks into the midst of which this igneous or 
melted mass had been protruded, if not crystalline before, 
would now become metamorphic rock, and to a great extent, if 
not fully, homegeneoHs and crystalline. Our sandstone would 
