910 REVIEWS 



fied shales and sandstones. In the same range, but on the 

 northeastern side, facing the valley of the San Pedro, another 

 formation of thinly bedded and highly crumpled mica schist in 

 sharply defined zigzag folds is referred to the Huronian, and is 

 given the name Arizonan. 



Hershey 1 describes the schistose rocks of the Klamath 

 Mountains in northwestern California. On the whole it seems 

 impracticable to fix upon any particular part of the time 

 between the Archean and the Devonian as the period of deposi- 

 tion of the Klamath schists, but it is believed that the evidence 

 favors the earlier or Algonkian portion rather than the Cambrian 

 or Silurian portion. 



Spencer 2 describes Algonkian rocks occurring in the center 

 of the Rico Mountains of Colorado. They consist of quartzites, 

 quartzitic schists, and biotite and actinolite schists. The exposed 

 thickness of the quartzites is over 350 feet and probably as 

 much as 500 feet. The relations of the quartzites to the schists 

 have not been ascertained. The schists and quartzites of this 

 area are similar in every way to the series of rocks exposed in 

 the upper part of the Animas Canyon and in adjacent portions 

 of the Quartzite or Needle Mountains, where they have been 

 referred to the Algonkian by Emmons and Van Hise. The 

 quartzite of the Rico Mountains is directly along the strike of 

 the great quartzite belt in the Animas Canyon and Needle Moun- 

 tain area. 



Jaggar, 3 in connection with the discussion of the laccoliths 

 of the northern Black Hills, incidentally refers to the structure 

 of the Algonkian. Its lamination abuts abruptly against the 

 hard basal Cambrian quartzite or the conglomerate, and has a 

 fairly uniform strike of north-northwest. The Algonkian surface 

 is seen to be warped. 



1 " Metamorphic Formations of Northwestern California," by Oscar H. Hershey, 

 American Geologist, Vol. XXVII, 1901, pp. 225-45. 



2 Twenty-first Ann. Rept. U. S. Geol. Surv., Part II, 1901, pp. 37-78; with geo- 

 logical map. 



3 "The Laccoliths of the Black Hills," by T. A. Jaggar, Jr., Twenty -first Ann. 

 U. S. Geol. Surv., Part III, 1901, pp. 171-303. 



