

Hunt.] 276 [January 2, 



names of Laurentian, Norian, (Upper Laurentian of Logan) Huro- 

 nian, and Montalban. Under these four heads we may conveniently 

 include all the crystalline rocks of that belt, with the exception of 

 the Taconian, to be mentioned farther on, although it is probable 

 that farther researches will enable us to establish other subdivisions. 



During a late journey across the continent he had been able to 

 make some observations on the crystalline rocks west of the 

 Mississippi, and to compare them with those of the Atlantic belt. 

 His examinations among the Rocky Mountains were made in the 

 Sangre de Cristo range near Garland ; and in the Front or Colorado 

 range at Glen Eyrie, in the Ute Pass, in Clear Creek Canon, and 

 about Georgetown. In all of these localities he found gneisses, often 

 hornblendic, but scarcely micaceous, and in many cases in large masses, 

 often granitic in aspect, with rarely interbedded gneissic layers. 

 These strata are penetrated in the vicinity of Georgetown by well- 

 marked granitic masses, probably exotic. The red granitoid rocks at 

 and near Sherman on the Union Pacific P. P. are probably gneissic. 

 These various rocks have all the lithological characters of the 

 Laurentian as displayed in the Laurentides, the Adirondacks, and 

 the South Mountain between the Hudson and Schuylkill Rivers. 

 Dr. Hunt here referred to the published observations in Hay den's 

 Report for 1873, of the late Mr. Marvine, who had studied these rocks 

 in the Colorado range and had then compared them with the Lau- 

 rentian. The speaker here mentioned the labradorite rocks having 

 the characters of the Norian, and associated, like that series in the east, 

 with large masses of titanoferite. These rocks, found in Wyoming 

 territory, were however, known to him only through specimens. 



The gneissic rocks of the Wahsatch range, as seen in the Devil's 

 Gate on the Weber River, are also Laurentian, to which are to be 

 referred the similar stratified rocks found in the same range farther 

 south, in the upper part of the Little Cottonwood Canon. Here, 

 among loose blocks of the gneiss, the speaker found occasional 

 masses of coarsely crystalline limestone with mica, and also varieties 

 of pyroxenic rocks characteristic of Laurentian; at the lower part of 

 this same canon there are, however, well-marked eruptive granites. 



The crystalline schists examined by the speaker in the foot-hills 

 at the western base of the Sierras in Amador, Placer, and Nevada 

 counties in California, have, according to him, all the characters of 

 the Huronian series as seen on the great lakes, in Eastern North 

 America, and in the Alps. The auriferous quartz veins in the coun- 



