Trafis. N. V. Ac. Set. 94 Feb. 12, 



distilled in the ordinary way. For roasting the Sotol, a pit is dug, some 

 ten feet in diameter and four feet deep, lined with rude masonry. In 

 this a fire is built, and when it has been burned down, the pit is filled 

 with several hundred Sotol heads. When roasted, they are chopped 

 in pieces and fermented in vats. 



Another interesting plant, the companion ot the Sotol, is the " Lechu- 

 guilla," {Agave heterocantha), of which the leaves furnish a strong 

 fibre, universally employed for ropes, sacks, etc., in Northern Mexico. 

 This grows on the mountain slopes, generally at an elevation of about 

 4000 to 5000 feet, is common in all northern Chihuahua, and especi- 

 ally abundant on the Chinati Mountains in Texas. 



GEOLOGY. 



The prevailing rocks of Chihuahua and Texas, are cretaceous sedi- 

 ments, chiefly limestones, broken through at frequent intervals by erup- 

 tions ot trap of various kinds, trachyte, porphyry, diorite, etc. Presidio 

 del Norte is surrounded by mountains, partly eruptive, partly upheaved 

 sediments, with open intervals between them, occupied by the cretace- 

 ous strata, generally much disturbed. Between Presidio and the Sierra 

 Rica, the middle and upper cretaceous rocks prevail — apparently the 

 Colorado and Laramie Groups, the lower shales with bands of calca- 

 reous concretions filled with fossils, the upper sandstones and shales 

 containing impressions of plants and thin coal. The concretions 

 referred to above contain immense numbers of well defined cretaceous 

 fossils, consisting of A)nnionitcs, Nautilus, Helicoceras, FtychoceraSy 

 Baculites, Gryphea, Ostrea, Inoceramus, etc. The Colorado shales here 

 are very black, though much metamorphosed, and containing Itiocera- 

 jnus, form the walls of the vein of the Sierra Rica mine, a clean cut 

 fissure, crossing the bedding of the shales nearly at right angles, hav- 

 ing a quartz gangue, containing some very rich but very compound ore, 

 copper, zinc, lead, silver and iron. 



Seventy-five miles southeast from Presidio are the San Carlos Moun- 

 tains, composed of cretaceous limestones set at a high angle and very 

 much metamorphosed. The San Carlos cafion cuts through the greater 

 part of the range, showing a section of several thousand feet of rock, 

 mostly light blue, but sometimes black limestones highly metamor- 

 phosed, yet often crowded with characteristic cretaceous fossils. 



The ore deposit at the San Carlos mine is of extraordinary magni- 

 tude and of special interest. It fills a series of chambers in limestone, 

 one of which is several hundred feet in length and more than 200 feet 

 in depth and breadth. It is evidently a chemical deposit, filling cavi- 

 ties made by solution, and consists of black, often crystalline magne- 

 tite, pyrites, galena, and blende, containing both gold and silver. Of 



