April 6, 1888.] 



SCIENCE. 



16- 



Rafael, where it crosses the Yaqui, the explanation is not so easy. 

 Approaching the river from the north, until within less than a mile, 

 the average drop is maintained. There, however, it gradually 

 diminishes until within about three hundred feet of the stream, 

 where it becomes simply a crack in the bluff which leads to the 

 river-bank. On the opposite side it recommences as gradually, but 

 nev^r attains the old width, not exceeding in any place over five 

 feet, and gently lessening, until at the point I abandoned it, nearly 

 five miles south of the river, the difference in level is a foot or less. 

 On this southern portion may be noticed two facts, — first, the 

 course is more directly into the mountains ; no longer hugging 

 their base, it strikes directly for their heart : next, and perhaps not 

 the least important, is the phenomenon of the hanging-wall eleva- 

 tion instead of depression. At the place I left off following it, a 

 division into two occurred, the split taking place at the foot of a 

 moderately high hill of reddish-looking metamorphic rock. Wheth- 

 er the fissure extends farther to the south, I cannot of my own 

 knowledge say. From some intelligent prospectors that went into 

 the Teras Mountains afterwards, attracted by the idea that such 

 terrestrial commotion ought to develop some leads of mineral, and 

 whom I asked to note any peculiarities observed, I learned that it 

 does extend about fifteen miles more to the south. From the 

 diminutive size of the fault where I last saw it, this seems to me 

 improbable. It certainly is not impossible, and the statement may 

 be taken sub jitdice. One thing is assured : the Teras Alountains 

 have been wofully broken up ; this I personally know. I have 

 been told by Colonel ICosterlitzky, who has recently been there, 

 that on the Chihuahua side of the Espuelas and Pitaicachi, is a 

 duplicate of the San Bernardino fault. I have endeavored to con- 

 firm this, but without success. 



"When I first viewed the end on the northern side of the river at 

 San Rafael, it seemed certain that there was the termination of the 

 rupture ; and it was not until one of my Mexican escorts had crossed 

 the stream, and hunted in the thick brush, that it was discovered 

 leading up the hill. The explanation of the diminution at this place 

 to a mere crack on each side of the river is not entirely plain to my 

 mind : therefore I leave the problem to you for solution. The rock 

 is indubitably involved in the slip at this point, although the drift 

 prevents it from being seen. If it was not, there could be no fault- 

 ing of even an inch, for it is not loose mesa drift, simply a slight 

 covering with the results of cliff denudation. The solid rock shows 

 close on both sides of the fault. 



" The pass through the mountains, where the Yaqui reverses its 

 course, is a very narrow one, three or four miles in length. The 

 walls are perpendicular on each side, rising to the height of several 

 hundred feet, and are composed, as are the immediate hills on the 

 north and the mountains on the south, of some reddish-gray look- 

 ing rock, probably eruptive. At the point where the river de- 

 bouches from the pass, and on the last bluff on the north, the fault 

 passes through its centre, becoming a mere crack. The pass is, or 

 was then, impassable, though some of the Me.xicans with me said 

 they had gone through it when the river was very low : at all other 

 times it is impossible to penetrate the gorge. 



" Some things to be noticed about the fault, in connection with 

 its sinuous course, are the small fissures at each bend with any 

 great degree of angularity. These occur on the salients of each 

 angle, but have no great length, in no place extending over a few 

 hundred yards, except opposite the Cabellera Mountains, where 

 there is a triplicate division over a mile in length. This gives the 

 main fault the appearance of having been compressed lineally from 

 the south, most of them having the free end to the north. They 

 are mostly ground-throws, not simply cracks. 



" From Pitaicachi to Cabellera Cafion the fault is far up on the 

 immediate foot-hills, and subsequently crosses them where there 

 can be no doubt as to a petrous substructure at slight depth. But, 

 as all of them are more or less extensively covered with debris, I 

 saw no spot in the face of the fault where a rent of solid rock was 

 visible. Neither did I follow it closely through this section, owing 

 to the weather when there. Thus I missed exploring the locality 

 of all others which might have illustrated the point at issue. No 

 one, however, who might stand and look over the ground at that 

 section could doubt, that, even if nowhere else there was slipping of 

 solid rock, here certainly there must be. A point which attracted 



my attention, and which seemed significant, was the appearance of 

 the foot-wall of the slip in many places, particularly where it abutted 

 closely on the mountains. This was the polished surface, as if the 

 same place had been the seat of similar perturbations in the past. 

 At these points the drift appeared to be more thoroughly consoli- 

 dated than at other localities. This striation and polishing began 

 within a few inches of the upper margin of the wall, — a place 

 where one would think slipping of the loosely aggregated mesa 

 drift would cause such an appearance. In addition, the fault at 

 these places usually was backed a short distance by the more dur- 

 able portion of the mountains, generally a bluff of some extent from 

 fifty feet to one hundred yards away. In no part of the line of 

 greatest drop is the fall less than eight feet, while in many places 

 it exceeds twenty. The estimated altitude of the mountains is, 

 Guadaloupes, Espuelas, and Cabelleras, about 7,000 feet ; the Teras, 

 9,000 to 10,000. 



" This, then, is a description of the big fault. We will now con- 

 sider the river-bed cracks and downthrows, for they come next in 

 size. Beginning about the San Bernardino Ranch, at the line, these 

 lesions exist as far as Granadas, which was as far south as I went. 

 These ruptures are not continuous. This form is most marked 

 about Batepito and Babispe. It is safe to say that the bed of every 

 water-course in the San Bernardino valley has changed level rela- 

 tive to the mesa from six inches to two feet. This has nothing to 

 do with the alteration of height as connected with, or caused by, 

 the great fault : that is additional. These river-bottom dislocations 

 seem to be a breaking-away of the bed from the enclosing mesa. 

 The mesas composed of drift are from twenty to one hundred and 

 fifty feet in height above the alluvial bottom, averaging perhaps 

 fifty. The cracks begin at or within a few feet of the base of these 

 terraces, and their course is that of the river-bed. The extent of 

 these from San Bernardino in a direct line I have told. They also 

 run from Bacerac to below San Miguelito, on the upper portion of 

 the Yaqui, but are lost sight of at that point. Whether this be 

 due to a total absence, or to the fact that the trail leads away from 

 the river, I cannot tell ; but from a short distance below San Miguel, 

 to a crossing called ' Pedregoso,' I saw none, at such points as we 

 struck the river in the line of the trail. These fords, however, 

 were at places where the nature of the channel would have pre- 

 vented any such phenomena, it being rocky and narrow. The 

 Fronteras valley, east of the San Bernardino, but tributary to it, as 

 may be seen by the water-course, was severely cracked up in the 

 same manner, but in a degree not to be compared with the two first 

 named . 



" In addition to these cracks and dislocations in the valleys 

 named, were lesions of another kind, — outbursts of sand and water 

 through fissures and small crater-like holes, a few inches to a foot 

 or more in diameter. This phenomenon was experienced in the 

 Sulphur Spring and San Pedro valleys in the United States to a 

 considerable extent, but not with the severity found farther south. 

 At Batepito Ranch, an area two miles long by one wide was four 

 or more inches deep with water immediately succeeding the first 

 shock on May 3. This was the greatest quantity of water thrown 

 up at any one place ; but the total amount must have been very 

 great, as the craters are met with wherever the river-cracks exist, 

 and sometimes where they do not. 



" The next class of fissures are simple cracks without depression 

 existing on the mesas. None of them are, as naturally would be 

 the case, through solid rock. They are many and extensive on the 

 mesas of the San Bernardino valley, and have a general direction 

 towards the main fault. Their width varies from an inch to a foot 

 or two, usually under a foot. 



" Next of the surface phenomena to be considered is the line of 

 devastation in the mountains. Here we find millions of cubic feet 

 of rock thrown down from the mountains to the canons and water- 

 courses below. Cliffs of solid crystalline rock are shattered and 

 split, as if a charge of giant-powder had been lodged carefully 

 amongst them for the express purpose of annihilating them. The 

 magnitude of the quake can be appreciated more by the evidences 

 of its force in the mountains than by the fault. The fault has the 

 appearance, and gives the idea, that it could not be helped : it simply 

 sunk, as Topsy growed. But the rending and splitting of such 

 masses as the mountain-cliffs impress one with a profound idea 



