Miscellanies. 407 



rocks, as to have subverted the origmal 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 subordinate 

 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 

 quandty of well defined primitive found in the vicinity, and by its 

 appearing at a lovt^er 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 indulge 

 some conjectures as to the mode of origin. The patches of secon- 

 dary limestone with shells, and the quantity of minute particles like 

 sand, which I suppose to have been cinders reduced to a level in the 

 plains, would indicate submarine volcanos, and in all probability, the 

 secondary limestone with shells could not be superposed on the vol- 

 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, so as not to pay for working unless the wages are exceed- 



