56 C. D. Walcott — Cambrian /tod's. 



includes bowlders of limestone carrying the Lower Cambrian 

 fauna. It is from 1,500 to 2,000 feet below the conglomerate 

 beds of Point Levis, which carry, in the lower beds, large 

 bowlders of limestone in which the Middle and Upper Cam- 

 brian faunas occur. By the fossils contained in the matrix of 

 the upper conglomerate series it is known that it is of Lower 

 Ordovician age, and from this it is inferred that the lower 

 conglomerate, carrying the Lower Cambrian fauna, occurs in 

 strata corresponding to the Upper Cambrian zone. The pres- 

 ence of these bowlder conglomerates of Upper Cambrian and 

 Lower Ordovician age proves that an orographic movement 

 occurred in the valley of the St. Lawrence by which the 

 Lower Cambrian and later Cambrian limestones were elevated 

 and formed a portion of the shore line during Middle, late 

 Cambrian and early Ordovician times. 



From my recent studies of the Cambrian rocks and faunas 

 over the interior of the continent, I conclude that the conti- 

 nent was depressed during the latter part of Middle Cambrian 

 and the early part of Upper Cambrian times, so that the sea 

 transgressed across the great interior of the continent and 

 deposited the sediments of the interior continental province. 



From the preceding statements it appears that toward the 

 close of Middle Cambrian time and during Upper Cambrian 

 time there was a decided continental movement, resulting in 

 the depression of the interior continental plateau, and that 

 this was accompanied by the formation of conglomerates of 

 the older Cambrian rocks in the valley of the St. Lawrence 

 and by a great deposition of sediments of later Cambrian 

 time in the Southern Appalachian region. In a paper soon to 

 be published by Mr. Arthur Keith of the U. 8. Geological 

 Survey evidence will be presented of an orographic movement 

 in Eastern Tennessee during this period. 



The fauna of later Middle Cambrian time, in Tennessee, 

 Georgia and Alabama, is essentially the same as that of the 

 basal Cambrian deposits about the Adirondack Mountains, the 

 upper Mississippi Valley areas of Wisconsin and Minnesota, 

 those about the Black Hills of Dakota, and the Llano Hills of 

 Texas. 



The fauna of the lowest horizon in Wisconsin includes Hyo- 

 lithes primordialis, Ptychoparia calymenoides, Agraidosif) 

 fecundus, Crepicephalus onustus, and Agraidos Woosteri. In 

 the next zone above, which is also included in the Middle 

 Cambrian, the following species occur : Lingula ampla, Lingu- 

 lepis pinnaformis, Obolella polita, Hyolithes primordialis, 

 Pemphigaspis btdlata, Agnostus sp., Crepicepthalus Texamis, 

 C. lowensis, Ptychoparia connata, P. optatus, P. (Loncho- 



