OCR Text |
Show 181 ance of diorite, bat has to be probably referred to the propylite of Riohthofen, although it is difficult to draw a line ox distinction between these two rocks, propylite being in many oases nothing bnt Tertiary diorite. Andesite.- A rock with a black vesicular matrix, containing imbedded well- formed crystals of orthoolase and hornblende, composes several peaks of the Paynte^ range about 28 miles east of the Colorado River, at Cottonwood Island. I have no doubt that it corresponds to Richthofen's andesite, a volcanic rook so prominent in theJSoath American Andes; whence its name. * Trachyte.- This is by far the most extensive of all erupted materials in California, and the varieties which it exhibits are numerous. Basalt, covering immense tracts in Arizona and New Mexico, dwindles hero into insignificance. The following list gives an approximate idea Qf the varieties met in various places of Southeastern California and adjacent regions: Locality. f Mohave Range < Cottonwood Island, ( Col- 1 orado River.) | / Dead Mountain, on thej Colorado River. | Black Cafion range, ( north S of the former.) J P& yute range. ....- CaUville.... Cncajmnngo P e a k . . . . . . . . .. SI DoTadcTCafion Bine Ridge Mountains,! Northwest Arizona. ] Detrital Valley, Northwest Arizona. Caves, Mohave River Val- J ley. | Saline Flats of the Mo- C have River. \ Grapevine Ranch, Mohave River Valley. Camp Cady, Mohave River Chnoka walla Peak Cafion Springs Matrix. Pink Brown, vesicular 1 Gray- brown Brownish- lilac Gray RedoJshpink Red Lilac Gray, vitreous Brown Pink brown.... Gray pink Brown, vesicular Light gray Gray, amygdaloid......... Green, vitreous Reddish Slate color Piok b r o w n . . . . . . . . . . . . . .. Nearly white, vitreous Light green Reddish, very siliceous.... Gray, v e s i c u l a r . . . . . . . . . .. Red, v e s i c u l a r . . . . . . . . . . .. Gray Gray, vitreous DarK gray Gray, vesicular Reddish Light g r a y . . . . . . . . . . . . . . . . Pink Red, with black stripes... 1 1 Imbedded minerals. Sanidino, biotite. Sanidine, ( sparingly.) Oligoclase and zeolite. Sanidine and hornblende. Hornblende, ( sparingly.) Qnartz, musoovite, orthoolase, and sparingly hornblende. Orthoolase. Oligoclaee and biotite. Many large orthoolase crystals, with little biotite. Red orthoolase and white sanidine. Biotite and sanidine. Oligoclaee and hornblende. Zeolite, with ( sparingly) hornblende. Large orthoolase crystals, sparingly hornblende. None. Sanidine and hornblende. Zeolites in the amygdaloid spaces. Oligoclase and biotite. Orthoolase and biotite. Orthoolase. Do. White orthoclane. Densely crowded with small crystals of feldspar, oiotite, and hornblende. Much sanidine and little biotite. Quart*, orthoolase, and biotite. None. Oligoclase and biotite. Large number o{ small sanidine crystals. Orthoolase. Biotite and aparingly oligoolase. Sanidine in large crystals. Little oligoclase ana hornblende, Orthoclase. Quartz, hornblende, and orthoolase. Sparingly sanidine and hornblende. Sanidine, ( sparingly.) Hornblende, oligoclase. None. That these trachytio outbursts did not take place at one and the same time, bnt were repeated at long intervals, becomes evident after even a cursory examination. Trachy-tic masses repeatedly forced their way np through the identical fissures, and examples of this kind are well exhibited at the Needles t in the vicinity of the cafion which the Colorado has cnt through the Mohave range. Here the strata of volcanic tufa show * A11 the different varieties of volcanic rocks mentioned in this report have been col* lected. Of a large number microscopical sections will be studied by a specialist in this branch. t These gigantic pinnacles, consisting of trachyte and trachytic breccia, have most probably obtained their singular shape by the erosive action of the river, when it was formerly running at a level of 1,000 feet and higher above the present bed. AP. JJ- 12 |