92 Bulletin of Laboratories of Denison University [Voi. xi. 
andesite and dykes of felsite and trachytic material cut the rock 
in a north and south direction, These dykes very commonly 
carry small quantities of gold and though most of the mines 
opened have been in very low grade ore the possibility is not 
excluded that valuable accumulations may occur. It has al- 
ready been mentioned that in the same area the east and west 
veins seem to carry lead and the theory is offered that this is 
due to the fact that dykes in this direction may be in commu- 
nication with the limestone region to the eastward. The lead 
is chiefly in the form of galena but, in several cases, a variety 
of vanadium compounds occur, especially in proximity to the 
north and south dykes. Several gold properties have been 
quite entensively worked but none of them in a way to really 
explore the dykes to an adequate depth. 
The whole area north of Magdalena to the Bear Mountain 
is of the same general character, while the latter seems to be 
the product of an enormous trachyte crater from which vast 
sheets have flowed in all directions covering a large area south 
of the Rio Salado. North of the latter is the margin of the 
great Cretaceous region of the Mount Taylor district which has 
been insufficiently explored along the southern margin. 
