484 HISTORICAL GEOLOGY. 



their relations to those of Keweenaw are not ascertained. Igneous outflows 

 occurred also in the Cambrian areas of southeastern Pennsylvania (G. H. 

 Williams, 1892). 



Foreign. — As in America, Cambrian beds are found along the borders of 

 the Archeean. They occur at various points in the northern part of the 

 Continent of Europe, from England along Sweden, Norway, Lapland, to 

 Esthonia, in Kussia, and also about isolated areas in France, Portugal, and 

 Spain ; the areas being the outcropping margins of Cambrian deposits. So 

 large a part of the European continent is under Mesozoic or Cenozoic strata 

 that geology cannot claim to know much about the actual distribution of the 

 Cambrian areas. 



Epochs of upturning in the course of the Cambrian. — Besides evidence of 

 slow change of level, evidence exists of one or more epochs of disturbance or 

 upturning during the long interval between the Archaean and the close of the 

 Cambrian. The evidence consists of superposition of the horizontal or nearly 

 horizontal beds of the Upper Cambrian on upturned beds of earlier Cambrian 

 in Minnesota, on the St. Croix, in central Texas, and in Arizona in the Grand 

 Canon of the Colorado. It is not known that any mountains were made at 

 the time in either of the three regions mentioned. In the Eureka district, 

 Nevada, the beds of the Upper and Lower Cambrian are conformable. 



Tide and currents the same essentially as note. — The beach material of the 

 early and later Cambrian was fine sands and pebbles, as it is now ; for these 

 are the materials of the beach-made rocks, — the Potsdam sandstone and 

 other like deposits. They were as quietly belabored by the waves, as the 

 ripple-marks show ; as free from extraordinary current movements, as proved 

 by the usual even regularity of the bedding. A reddish variety of these 

 sand-made rocks, spread out and accumulated on Cambrian beaches or sand- 

 flats, is used in American cities as one of the kinds of building-material. 

 The waves and currents were then as quiet in their work about the Adiron- 

 dack shores as they are now on the New Jersey coast. No evidence exists 

 that the world's tides and currents had greater force than in this modern era 

 of a quiet earth. 



Climate in the Cambrian. — The evidence as to climate open to the geolo- 

 gist is that based on the kinds of life represented by fossils in the rocks. 

 The Cambrian fossils thus far studied are from temperate latitudes only. 

 Nothing is gathered from them as to different zones of temperature in the 

 ocean, and nothing that proves the temperature of the waters to have been 

 warmer than that of the existing torrid and warm-temperate zone. We have, 

 therefore, to regard the climate, as well as the tides and waves, to have been 

 such as now characterize the warmer portions of the existing world. There 

 was no frigid zone, and there may have been no excessively torrid zone. 



Purity of the air and waters. — The purification of the air and waters 

 through the making of limestone, which commenced in the later part of 

 Archaean time, continued through the Cambrian; for limestones are common 

 rocks in the series, though far from being the only ones. The degree of 



