424 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



mesa-topped ridges, covered by Pleistocene beds and underlaid by 



upturned beds of earlier Tertiary, whose age lias not yet been deter 

 mined. The view of the Sawateh Mountain peaks to the northwest 

 and Mount Ouray on the west is here very hue. 



The hills on the eastern side of the Arkansas, for several miles above 

 and below Salida, are mainly composed of a series of crystalline schists 

 and some more massive bands, which have been referred to the Algon- 

 kian period.* The known exposures of this series of roeks extend 

 from a point about four miles ((> km.) north of Salida southward along 

 the eastern bank of the river to where it bends east into the sedimen- 

 taries, which cover them, and thence westward into the north end of 

 the Sangre de Cristo range. Immediately opposite Salida andesitic 

 breccia conceals the schists for nearly one mile (1.61 km.) back from the 

 river, and at six miles (10 km.) or more the sedimentary rocks in rem- 

 nants are found on the edges of the schists. Their outcrops to the 

 north are limited by andesitic breccia. 



As now r known, these schists are derived from eruptive rocks of at 

 least two kinds, one acidic and one basic, which originally succeeded 

 each other in a long series of alternating tlows, probably with toffs or 

 fragmental deposits of the same materials in certain places. The most 

 massive rocks now preserved are those occurring in the Arkansas val- 

 ley below Salida, and the most altered schistose forms are at the north- 

 ern extremity of the known section. Here are tine schistose rocks 

 variously characterized by mica, chlorite, garnet, staurolite, and various 

 amphiboles. One loose-libered actinolite schist is locally so impreg- 

 nated by copper ores that the material has been mined at a profit. The 

 principal mine, the "Sedalia," is situated on the hillside facing the 

 Arkansas valley, about three miles (5 km.) north of Salida. In a chlorite 

 schist adjoining the copper-bearing layer occur the huge dodecahedral 

 garnets which have been so widely distributed over the world through 

 mineral dealers. 



[By S. F. Emmons.] 



Below Salida the Arkansas valley changes from a southern to an 

 eastern course, across the southern extension of the Mosquito or Park 

 range to the Colorado or Front range. 



At Cleora the valley narrows and the road passes over the more mas- 

 sive rocks of the schistose series into Lower Paleozoic beds, dipping to 



"In the month following the evenrsion <>f the OongreM the -writer was alilo to 

 examine, in some detail, the schistose series in question, and the statements as to 

 its character here given are based on this recent study. The strata visited by 

 some of the geologists in the ravine cast of Salida belong to the most thoroughly 

 metamorphosed part of the series, and their origin is clear only through the inter- 

 mediate stages found in other parts of the section. 



