ENDLicH.J GEOLOGY — SAN LUIS DISTRICT, SECTION B. 327 



brown argillaceous shales and isolated strata of limestones, (<s,) with, 

 fossils. Near station 19 one of these was exposed, and crinoids were 

 found. The remainder is made up again by Arkansas sandstone and a 

 few limestones, all Carboniferous, the combined thickness of which, 

 with those underlying, probably exceeds a mile. Although it was pos- 

 sible to see over to the east side of the slope for some distance, but little 

 detail could be observed, and the section, therefore, shows nothing but 

 the lower strata. The course of the section is about noith 70° eastc 

 Proceeding farther northward, to station 20, it was found (Plate XIII, 

 section B) that the granite {a) had again appeared, and forms the highest 

 peaks at that locality. As far as could be determined, the Arkansas sand- 

 stone (b) rests upon the granite for about 2,000 feet, although I have but 

 little doubt that it is underlaid by still older formations even at that point, 

 but the amount of debris that is deposited at the base of the mountains 

 obscures the line of junction. In ascending the west slope to reach station 

 20, the boundary -line between the granite and sandstone was found to be 

 well defined, the latter ending with a little swell in the outline of the 

 mountain. At that point its dip is almost vertical, but soon diminishes; 

 a section may serve to illustrate the conditions observed. A heavy 

 bed of dark, almost black, shales (d) overlies the sandstones, and is in 

 turn covered by a series of sandstone strata, [b.) Toward the base of 

 the mountains some limestone makes its appearance, slightly disturbed, 

 but originally conformable with the sandstone. The eastern slope is 

 mainly composed of the latter. In speaking of this station, 20, it may 

 not be out of place to mention a phenomenon which, although not 

 strictly appertaining to geology, may be of some interest; During our 

 trips in the higher mountains we had several times noticed evidences of 

 the presence of comparatively large quantities of electricity, but on this 

 station anything thus far experienced was surpassetl. It was found 

 that as soon as a sufficient amount of electricity was contained in the 

 atmosphere, any metal instrument or weapon that may have been about 

 would produce a buzziug sound, like the hammer of an induction-coil. 

 When the supply of electricity in the lower strata of air was exhausted 

 and the buzzing ceased, it could be renewed by holding the instrument 

 up higher into the air. On this particular instance, a heavy gale was 

 blowing from the north, driving a storm toward us with great rapidity. 

 The wind came in single puffs, and while a rifle that was carried along 

 would not buzz during the short lull of the wind, it would do so quite 

 strongly as soon as the gust reached the point of observation. At one 

 time the quantity of electricity grew so large and intense, that I received 

 from my rifle a shock sufficient to paralyze me momentarily. The 

 weapon dropped out of my hands, and about half a minute after a 

 discharge of lightning took place very near by, by which the electric 

 phenomena were quiett-d for a time. Soon, however, electricity accu- 

 mulated again ; its manifestation again became inteuser, until every 

 hair on the head was rising upward ; every finger buzzed when held up 

 into the air, and every pointed rock hummed with a sonorous sound. 

 As soon, however, as the next discharge took place, this time some dis- 

 tance off, it again subsided. From personal communication it has been 

 found that these occurrences have been noted by a number of persons, 

 who perhaps either had no opportunity of making them known, or 

 deemed them of too little importance. 



As the diluvial and alluvial material begins right at the basis of the 

 west slope of the range, it could not be determined with certainty 

 whether the Carboniferous strata extend to the westward for any con- 

 siderable distance ; but about eight miles west of the termination of the 



