PALEOZOIC TIME — CAMBRIAN. 483 



111 India, the Director of the Survey reports the discovery, by Dr. Warth,. 

 of two Trilobites in the Neobolus beds of the Salt Range, and the identi- 

 fication, by Dr. Waagen, of one of them as a species of Conocephalites, and 

 of the other as probably an Oleniis; thus indicating the presence of a Cam- 

 brian and probabh' Lower Cambrian fauna. 



Species of Conocephalites, Dicellocephalus, Ethviophyllum, and several 

 other Cambrian genera, have been discovered in the rocks of South Australia. 



Kayser described, in 1876, a number of Brachiopods and an Olenus from 

 the northern part of the Argentine Republic, thus indicating Upper Cambrian 

 rocks in South America. 



GEOGRAPHICAL AND PHYSICAL CONDITIONS AND PROGRESS. 



Amencan. — Cambrian history, as the facts presented show, is the history 

 of a begun and a growing continent ; growing not by extension seaward, but 

 by progress in rock-making over its wide surface wherever sufficiently sub- 

 merged, and in rock destruction over emerged areas as a source of material 

 for the new rocks. The abundance of shells of Pteropods may seem to 

 indicate deep waters, since they now abound in sea-bottom deposits at depths 

 of 100 to 1000 fathoms in the seas of the Mexican Gulf. But these pelagic 

 species live at or near the surface ; and if any physical conclusion is to be 

 inferred from their abundance, it is simply that the surface of the water 

 was between 70° F. and 85° F. 



The gathering of building-material in gradually deepening geosynclines 

 or troughs for future mountain ranges in the neighborhood of the Appala- 

 chian and Rocky Mountain protaxes has been stated to have commenced 

 (page 357) with the beginning of Paleozoic time. The Cambrian formations 

 bear testimony to the fact ; for they have a great thickness, thousands of 

 feet, over the sites of the Taconic and Appalachian ranges, west, for the most 

 part, of the eastern protaxis, and over that of the future Laramide or post- 

 Cretaceous Range, partly east and partly west of the western protaxis. Even 

 in the Lower Cambrian a large part of this thickness was attained ; while 

 through the interior basin of North America, as far as the facts are known, 

 the Cambrian is thin, and the Lower and Middle Cambrian wanting. Wal- 

 cott's map, in the U. S. G. S., Tenth Ann. Report, presents the probable con- 

 dition, and sustains his view of very uniform conditions over the interior, 

 which signifies either emergence of the land or but small submergence, and 

 no subsidence in progress. 



In the Lake Superior region, along the southern margin of the Archaean V, 

 between it and the Archaean area of Wisconsin, there was one great exception 

 to uniformity over the interior continental area. But it was apparently con- 

 fined to the Keweenaw area, where there were extensive igneous eruptions. 

 The igneous rocks of Isle Royale, in Lake Superior, are referred to the same 

 epoch by Whitney. Similar ejections took place also in Michipicoten Island, 

 and at Thunder Bay and other points along the north shore of the lake ; but 



