NE-SAW-JE-WON 



these soft beds are deeply carved and gouged out along their 

 exposures they may be likened to "moats" between the ram- 

 parts of harder rock. 



Without going into detailed descriptions of each set of rock 

 bowls, let us rather consider their relation to the development 

 of the basins of the Great Lakes. As flowers, trees and people 

 have distinctive family names, so names have developed to 

 designate the rock formations. English geologists first studied 

 the sedimentary rocks in England and Wales, and the names 

 given the formations there have now been applied all over the 

 world to rocks which have the same relative positions and are 

 similar in character and in the life records or fossils contained 

 in them. The lowest and oldest of the sedimentary rocks 

 known to the early geologists were named Cambrian, from 

 Cambria in Wales where they were first studied. For con- 

 venience, all the older igneous and metamorphic rocks are 

 grouped as pre-Cambrian. Above the Cambrian, in parts of 

 North America but not in Europe, is the Ozarkian, named 

 from the Ozark Mountains; the next set of higher and younger 

 rocks is the Ordovician, named from an ancient tribe of 

 Wales; over the Ordovician rocks are the Silurian, also named 

 from an ancient tribe of Britons that lived in Wales; then 

 come the Devonian, commemorating Devon in England; and 

 above these are the Carboniferous rocks — the Mississippian 

 and the overlying Pennsylvanian. (Figure 1.) 



Insofar as the Great Lakes are concerned, the important 

 facts about the rocks are their arrangement and position and 

 their different degrees of hardness. The pre-Cambrian rocks, 

 which are hard and resistant to weathering, are downwarped 

 to form the basin of Lake Superior. The Cambrian is a very 

 resistant, coarse sandstone underlying the Ozarkian sandy 

 dolomite, dolomitic sandstone, and dolomite. The thin edge 

 of the Cambrian or Lake Superior sandstone, which once 

 rested upon the pre-Cambrian rocks, has been weathered away 

 until now its northern edge stands as the outer rampart of red, 



14 



