APPENDIX—GEOLOGICAL SURVEY. 
397 
mineral veins with their deposits of ore without reference to 
water as the medium in which this material has been prepared, 
and through which it has been brought into the fissures, and 
held subject to the chemical conditions that have brought it 
into its present crystalline form. 
Along these lines in the earth’s crust where such conditions 
are known to have existed, and where evidences of their past 
activities still remain (although like fossils in the rock) are 
the lines in which our mines and productive mineral veins 
are found, and they are found only along such lines. They 
are, indeed, as much the isothermal lines of the past that mark 
the distribution of temperature, and conditions necessary to 
the production of mineral veins, as are the isothermal lines of 
the present, that mark the distribution of temperature and con¬ 
ditions necessary to vegetable production. 
In our examinations of mineral strata then, or in explora¬ 
tions of the country for mineral regions, no surer guide can be 
furnished us than the evidences of the action of these physical 
forces and conditions. The disturbed and peculiar conditions 
of the strata along lines where these* evidences are found fur¬ 
nish most, if not all, the material of our knowledge, from 
which all practical as well as scientific deductions are made. 
Hence the importance of presenting in my report, in as clear a 
light as possible, the phenomena of the lead district, that the 
physical conditions and forces of which they are the result 
may be apparent, and that deductions, both scientific and prac¬ 
tical, may be made properly. 
But, before I enter fully on the description of the phenome¬ 
na of the lead district, allow me to trace a little further the 
analogy between these two departments of nature. It will en¬ 
large our views, and clear our conceptions of natural phenom¬ 
ena, and enable us to recognize more distinctly the laws that 
underlie them as their cause. 
We know that the vegetable and mineral kingdoms meet in 
the crust of the earth ; the materials of which vegetables and 
minerals are composed are in many respects the same; both 
are the result of physical conditions; and in these conditions 
