NOETH AMERICAN GEOLOGY. 211 



studies that some of the crystalline rocks of the coast ranges are altered 

 sandstone of Cretaceous age.* Dale gives other instances of the meta- 

 morphism of the Carboniferous of Khode Island to gneisses and mica 

 scliists.t Emerson, in a paper before the American Association, dis- 

 cusses in detail the relations of the Helderberg limestone and the crys- 

 talline condition of overlying as well as of underlying rocks in the Con- 

 necticut Valley;! ^^^ the studies of Van Hise on the enlargement of 

 mineral grains suggests an easily understood explanation of the forma- 

 tion of many of the crystalline rocks of post-Archean age. With all 

 this evidence in view, it now seems probable that the whole controversy 

 about our metamorphics will end in finding that, while the greater mass 

 of them belong to the Archean and its subdivision, there are areas of 

 considerable size which will prove much younger. 



There are now in progress three systematic surveys of the crystalline 

 rocks. Pumpelly in the Appalachian belt, Irving in the Great Lake 

 district of the Northwest, and Britton in the New Jersey Highlands. 

 During the past year the two latter have published preliminary reports, 

 Irving for 1883 and Britton for 1885. 



67. The principal features of Irviug's reports are accounts of a re-ex- 

 amination of the typical Huronian, studies of a number of series which 

 are correllated with tbe Huronian, and a discussion of equivalency. The 

 typical Huronian is found to consist primarily of quartzite, with occa- 

 sional beds of graywacke, limestone with chert, and numerous eruptive 

 greenstones, the whole being very gently flexed and unconformable to 

 the older gneisses. With this formation are correllated the Marquette 

 and Menominee, and the Peuokee-Gogebic iron-bearing series, the 

 schists and quartzites of the Upper Wisconsin Valley, the slate-belt of 

 the St. Louis and Minnesota Rivers, the quartzites of Cippewa and Bar- 

 ren Counties, Wisconsin, the schists of Black River Valley, the Baraboo 

 quartzites, and those of southern Minnesota and so.itheastern Dakota, 

 and the Animikie series. The folded schists north and east of Lake 

 Superior are thought to be equivalent to at least the latter. § 



as. Bell, in a report on the Hudson's Strait and Bay, describes the 

 crystalline rocks of that district, and states that the schistose members 

 classed as Huronian are either interstratifled with the massive beds of 

 the Laurentiau system, or conforu) able to them. The quartzites of the 

 typical Huronian district do not extend far to the north and west, and 

 the schistose series includes, besides a great variety of crystalline schists, 

 more or less massive diorites, argillaceous and dioritic slate, conglom- 

 erates, granites, syenites, schistose and jaspery iron ores, limestones 

 or dolomites, and imperfect gneisses. As far as observed, they are much 

 more abundant in the region between the Great Lakes and Hudson's 



*Am. Jour. Sci., in, vol. 31, pp. 348-357. 



t Canadian Inst., Proc, vol. 3, pp. 18-22. 



t Proceedings, Vol. 35, pp. 233. 



^ U. S. Geol. Survey, 5tli Aunnal Report, pp. 175-282. 



