78 The Cambrian Rocks of North America. 



underlying Taconian quartzites, marbles and schists (Lower 

 Taconic) which the author regards as pre-Cambrian, and the 

 still older crystalline schists of the Atlantic belt, including those? 

 chiefly of Huronian age, which have been called " Altered Quebec 

 group. " 



The name of Taconic cannot be retained for the Appalachian 

 Cambrian, which was, as early as 1861, correctly claimed by 

 EmmoDS as belonging to the period of the first fauna. The 

 Hudson-R,iver group, as originally defined, included the whole 

 of the Appalachian Cambrian, with some portions of the under- 

 lying Taconian, and others of overlying Ordovician strata, from 

 which, in the Appalachian area, their characteristic limestones 

 are wholly or in great part absent. It is solely from this 

 association with the Cambrian Graywacke of strata of Loraine 

 age that the Hudson-River group has come to be regarded as the 

 palseontological equivalent of the Loraine shales. 



In the stable and little disturbed area around the Adirondack 

 mountains, including the Cham plain and Ottawa basins, the 

 Cambrian is represented only by the quartzites and magnesian 

 limestones of the Potsdam and Calciferous divisions, which are 

 shallow-water deposits, corresponding apparently to small portions 

 only of Cambrian time. The physical conditions of the Missis- 

 sippi area appear to have been similar to that of the Adirondack 

 region. As seen to the west of Lake Superior, the lowest Pots- 

 dam beds of Hall rest unconformably upon the great Keweenian 

 or copper-bearing series. This, although containing, as the 

 speaker had elsewhere shown, some evidence of organic life, pro- 

 bably worm-burrows and sponges, cannot be claimed for the 

 Cambrian till it shall have been shown to contain a Cambrian 

 fauna. 



In this north-western area we find, moreover, beneath the 

 Cambrian horizon, representatives of the Lauren tian and of 

 the Norian ; the latter in the typical norites, or so-called gabbros 

 which, near Duluth, are directly overlaid by the Keweenian, else- 

 where resting on Laurentian or on Huronian rocks. There are 

 also found in Wisconsin petrosilex-rocks of Arvonian type, with 

 quartzites, rising from beneath the Cambrian sandstones. Typi- 

 cal Montalban and Huronian rocks also occur around this area 

 besides the group which the speaker long since called Animikie, 



