SANDSTQNES OF THE MIMBRES — PICACHO. 157 



There is no other thermal spring known in this locality ; to the east, several cold springs 

 ooze out, and run a few yards down the valley, forming collections of carrizo or tule, the only 

 vegetable growth in this region of barrenness. Notwithstanding the disturbed character of the 

 region around, there is nothing to justify the conclusion that there is at the present time any 

 volcanic forces in action ; nor can this spring be supposed to bo caused by any such existing 

 force. The presence of an excess of carbonate of lime may have been obtained by the spring 

 passing through the strata of carboniferous limestone, which may be presumed to underlie the 

 sandstones of the surface ; if this be so, the temperature should then be due to the depth from 

 which the water has arisen to reach the surface ; the temperature of the water, however, is an 

 argument against the latter, as it is 70° above the ordinary temperature, which would be 

 equivalent to a depth of 3,780 feet below the surface. 



Northeast of "Agua Caliente," between it and the river, is an upheaval of felspathic porphyry, 

 which has carried up the sandstone strata on each side, which dip northeast and southwest. 

 The upheaval itself presents the appearance of a battery or fortification presenting its semi- 

 circular point to the south. At some distance from this upheaval immense blocks and loose 

 masses of sandstone rock lie heaped together in the most grotesque forms ; some of them consist 

 of several masses, one piled on another, and in some instances nicely balanced and ready to 

 topple; seen from a distance, in this highly refracting atmosphere, now they resemble trees, and 

 now men ; least of all would they be taken for really what they are, disintegrated sandstones. 

 They are now known as the Giants of the Mimbres. The wearing away of these grits, whitish 

 and yellow sandstone, such as are described near Ojo de la Vacca and the Mimbres, show what 

 a loose texture these rocks have ; every heavy shower denudes them to some extent, and after 

 some years they have no longer the same appearance or outline which they formerly showed. 



From the Rio Mimbres to the extremity of the Picacho de los Mimbres is ten miles, and thence 

 to Cook's spring, eight miles, the trail passes at the southern j^oint of the hill ; the intervening 

 country is rolling land, not broken through by any extensive outcrop of volcanic rock ; a 

 natural section afforded by the Mimbres at the point where the trail from camp, August 10th, 

 passes east to the Picacho, showed the porphyritic masses, forming the low rugged hills on the 

 east of camp ; and upheaved by these, and exposed to view by the wearing of the edge of the 

 river valley, were the red and white sandstones and grits, already described at Ojo de la Vacca. 

 These sandstones were exposed about a half mile south of the erupted hills, and dipped away 

 from them south 12° east at an angle not exceeding 12°. 



The rock nearest to the volcanic mass, and situated lowest down, was the red sandstone, with 

 30 feet exposed. Above it was the whitish grit, 50 feet exposed ; and some few yards further 

 south, another small butte was composed of the whitish yellow sandstones, dipping south at a 

 small angle. 



The Picacho de los Mimbres forms a very prominent landmark, both from its height and 

 irregular conical form ; it is 2,500 feet above the plain, about ten miles long, and stands uncon- 

 nected with any other range, and is distinctly visible from the summits of the Organ mountains 

 on clear days. It has an axis of reddish granite and syenitic rock. The felspar is red in 



aod no ochreous or mucilaginous deposit had taken place. It was faintly acid to litmus in the spring; from these properties 

 it may be inferred that the water was not of a mineral character, the acidity being due to the carbonic acid, partly dissolved 

 and escaped. In Mr. Bartletfs " Personal Narrative," when noticing this spring, the gas is stated to be nitrogen ; this is a mistake. 

 The water is highly charged with carbonate of lime, held suspended by excess of carbonic acid gas; at the high temperature 

 of the fluid when reaching the surface, the latter is thrown off in bubbles, and the carbonate of lime no longer held in solution 

 is thrown down, to form the sides of the basin. T. A. 



