202 GEOLOGICAL SURVEY OF THE TEEEITORIES. 



aration of their two present walls, a separation that was not gradual, 

 such as would be produced by the erosive action of flowing waters, 

 but a sudden one. From Lost Trail Creek eastward the lower members 

 of the trachytic system can be readily traced for many miles. The dip 

 is constant in the direction the river flows, but slight. If time could be 

 spared for a careful investigation of the volcanic rocks along the Rio 

 Grande much valuable information regarding their horizontal and ver- 

 tical distribution could be obtained. The extent of the single flows, 

 characterized as such by their stratigraphical relations and lithological 

 character, is truly astonishing, and basing uj)on this and other evidence, 

 I have come to the conclusion that the volcanic area surveyed by our 

 l^arty in 1873 is but the continuation of the one under mention at pres- 

 ent. 



Flowing in a northerly difection is White Earth Creek, which has re- 

 ceived its name from the exposure of trachyte Xo. 1. Ascending from 

 station 6 the caiion is found to be walled in by vertical or nearly verti- 

 cal blulfs of No. 2, while metamorphic rocks crop out below. As usual, 

 they present the rugged appeitrance common to members of that num- 

 ber, until the small valley north of station 2 is reached, where the flows 

 have preserved more of their original form, and show plateaus of no 

 very considerable extent, however. Above the first lower plateau two 

 more are found, until finally a slope is reached leading up to the station, 

 an elevation of 13,r>G0 feet. Here the rock corresponds to some of the 

 members of the higher No. 3. The paste of this rock is compact, 

 darker than that of the corresponding group generally. Numerous 

 crystals of yellowish sauidite occur in it, while mica is wanting almost 

 entirely. 



Descending again to the level of the creek, it is found that the strata of 

 No. 1 crop out for some distance along its left-hand bank. The rock 

 here is white to grayish and yellowish, readily decomposed. It is not 

 so firm in texture as that on the Rio Grande, and therefore does not 

 show the picturesque forms that were observed at that point. Higher 

 up the succeeding numbers set in until No. 3 is reached. At all these 

 localities the blufl' character is well preserved. At many places the 

 rocks are bare of any vegetation or soil, and the traveler rides over the 

 surface, as it formerly flowed, only with the difference that at i)resent 

 it shows an easterly dip. Ascending still farther, toward stations 3 

 and 4, basalt sets in about 400 feet in thickness at the edges of the 

 continous blufl'. A long, high i^lateau, some distance above tim- 

 ber-line, stretches from north to south approximately. No soil has 

 accumulated as yet on the naked fragments of vesicular basalt. Nu- 

 merous little ponds and swamps indicate that beneath the layer of 

 fragments, the original flow must be undisturbed. Two varieties of 

 basalt occur here, the black and a brownish-red. No definite rela- 

 tion between the two could be recognized, and it seems highly im- 

 probable that it should exist. Both ai'e vesicular, sometimes hav- 

 ing the vesicles drawn out to one or two inches in length. Olivine, 

 a dark-gieen variety, is found sparingly in their raicrocrystalline paste. 

 Indications of columnar structure may be observed along the precipitous 

 blufl' on the west and southwest sides, but the columns are not well 

 developed. Station 5, at an elevation of 12,737 feet, is located a little 

 west of south of the two last-named stations, on a similar plateau, which • 

 at one time was iirobably in connection with it. 



These plateaus separate the waters of White Earth from those of 

 Lake Fork Creek. Near the northern line of our district, between the 

 two last-named creeks, station 7 was located on an isolated i^atch of 



