210 RECORD OF SCIENCE FOR 1886. 



limestone, brought up by a fault against the Hudson River slates. 

 The thickness exposed is about 300 feet. He suggested that the fault 

 may be related to the great dislocation of Logan, as it ranges NNE. 

 and SSW., and has been traced for some distance.* 



65. The stratigraphy of the Cambrian of the Northwest is discussed 

 by Wiiichell from recent observations in the valley of Minnesota. The 

 following table represents his conclusions in regard to the relations of 

 the several sandstones and limestones constituting the Cambrian of 

 Minnesota and Wisconsin : 



St. Peter's sandstone. 

 Shakopee limestone. 

 New Eichmond beds 

 Main body of limestone. 



^ Jordan sandstone (Potsdam!). 

 04- i^^^i^ \ St. Lawrence limestone. 

 ^^•^^«^^i Shales. 



[Dresbad sandstone (Potsdam?). 

 Shales. 



Hinckley sandrock (Potsdam ?). 



Red shales and red sandrock, passing into the Cupriferous ? (Pots- 

 dam ?).t 



66. Dawson, in his report on the Canadian Eocky Mountains, de- 

 scribes the Cambrian of that district. The rocks consist in the main of 

 11,000 feet or more of quartzites and quartzitic shales passing into ar- 

 gillites, and including occasional beds of limestone, conglomerate, and 

 lava flows. A few Middle Cambrian fossils were found in its upper i)art, 

 but with this exception the series is closely similar to the quartzites and 

 argillites of the Wasatch and the Chuar and Grand Caiion group of 

 Arizona. | 



ARCHEAN AND METAMORPHIC. 



The crystalline metamorphic rocks of the United States have been 

 subjects of controversy almost from the first; and although much has 

 been written about them, they have received systematic study at com- 

 paratively few localities. In the Appalachian belt there have been 

 those who considered the rocks of some areas to be Cambrian, Silurian, 

 and Devonian in age, the evidence for which from its own character and 

 the recent revelations of the possibilities of paramorphism and metamor- 

 j)hism seems almost incontrovertible ; while on the other hand many ge- 

 ologists hold, at least tentatively, that all metamorphic crystallines of 

 considerable areal extent are Archean. In the studies of the past year 

 some of the areas thought to be iiost-Archean metamorphics are found 

 to be shore lines of Cambrian formations, and consequently pre-Cam- 

 brian ; while Becker, in California, finds as a result of careful detailed 



* Am. Jour. Sci., in, vol. 31, pp. 125-133. 



t Fourteentli Aimiial Report of the Minn. Geol. Survey, pp. 325-337. 



t Canada Geological Survey, Report for 1885. B. 



