Miscellanies. 407 
rocks, as to have subverted the original order of nature and to change 
the class every mile; this leaves the geologist in doubt concerning 
the substrata, and would reduce most of his investigations to hy- 
pothetical results... The brilliancy of the precious metals has'so fixed _ 
the attention of all travellers, miners, and mineralogists, that the only 
specimens to be met with are derived from what they call veinstones; 
so true is this, that a gentleman who wished to acquire a little knowl- 
edge of geology, could not find in Mexico a specimen of granite, 
gneiss, or mica slate; any assortment of rocks, to be found here, 
comes from Fryberg in Germany. From this great scarcity of ma- 
terials, and still greater difficulty of procuring them, any thing resem- 
bling a general description must be a hypothesis formed from the 
small spots above the principal mines that have been wrought in fol- 
lowing the metallic veins to a great depth. 
From the great range of the Andes, spring all the Do rincrs 
mountains, forming large plains or valleys either near their summit 
or on the planes of their descent on either side, on which planes, be- — 
low the level of the principal range, when not covered by the vol- 
canic formations, the greatest part of the primitive crops out to day. 
On the tops, both of the great range and the subordinate heights, 
appears to be placed the seat of the mines, principally in transition, 
though some are thought to be in primitive shist or marble, from 
-which it would appear, that the summits of the mountains are prin- 
cipally transition. This supposition is countenanced by the small — 
quantity of well defined primitive found in the vicinity, and by its . 
appearing at a lower level on both sides; this seems to indicate that 
the primitive is the formation of the whole range. Having gone so 
far without sure footing, the speculation may, be pushed a little fur- 
ther for our amusement if not for our instruction, while we mavice 
some conjectures as to. the mode of origin. The patches of sees 
dary limestone with shells, and the quantity of minute particles like 
sand, which I suppose to have been cinders reduced toa Jevel in the 
- plains, would: indicate submarine volcanos, and in all jility, the 
secondary limestone with shells could, not be superposed < ‘on the yol- 
canic by any agent except water, and the quantity of cinders that 
would be formed by the quick. cooling of the lava by ejection into 
the sea may be. considered-as a collateral proof. 
' Most-of the veinstones, I have seen, which are the principal speci- 
mens in all collections; are secondary ; generally very poor in the use- 
ful metals, ad as not to pay for working unless the wages are exceed- 
