2 STKATlGRAPHlCAL GEOLOGY. 



The names used in American Geology, for the purpose of the classification 

 of the strata into groups, have been derived, generally, from the localities at 

 which the rocks have been studied and described. This method of nomenclature 

 is preferred to any other, because the name itself can never mislead as to the 

 mineral structure or relative position of the rocks, and the geologist may visit 

 and study the locality with the certainty that he is investigating the typical 

 group. Prof. Rogers conceived the idea of improving the nomenclature of the 

 palasozoic rocks by dividing them into fifteen parts and giving them names sig- 

 nificant of their relative ages. This he did by using words suggesting meta- 

 phorically different parts of a da^-, as follows: Primal, Auroral, Matinal, Le- 

 vant, Surgent, Scalent, Premeridian, Meridian, Post Meridian, Cadent, Vergent, 

 Ponent, Vespertine, Umbral and Serai, meaning respectively the formations of 

 the Dawn, Daybreak, Morning, Sunrise, Mounting Day, Climbing Day, Forenoon, 

 Noon, Afternoon, Declining Day, Descending Daj', Sunset, Evening, Dusk and 

 Nightfall. Unfortunately for his attempt to substitute another, for the geographi- 

 cal nomenclature then quite well established and susceptible of indefinite ex- 

 pansion, without the use of conflicting terms or words that could mislead the 

 student, there were several extensive groups of rucks full of the remains of ani- 

 mal life, as yet unexplored, and consequently quite unlinown to his system. 

 For obvious reasons the nomenclature suggested liy jNIr. Rogers has not been 

 adopted, and in all probability never will be. 



The Archfean formation is divided into theLaurentian and Huronian groups. 

 The Laurentian series of metamorphic rocks forms the base of the geological 

 column, and has an estimated thickness in Canada of 32,750 feet. It takes its 

 name from the Laurentian mountains of Canada. The liozonn canadense, a 

 fossil Rhizopod, is found at the base of the Grenville band of limestone, which is 

 near the middle of this series. The estimated depth of the Laurentian series to 

 the lowest place at which this fossil has been found is 16,500 feet. Sir W. E. 

 Logan describes the Grenville band as follows : 



"The general character of the rock connected with the fossil produces the 

 impression that it is a great foramiuiferal reef, in which the pyroxene masses 

 represent a more ancient portion, which having died, and become much broken 

 up, and worn into cavities and deep recesses, afforded a seat for a new growth of 

 foraminifera, represented by the calcareo serpentinous part. This in its turn be- 

 came broken up, leaving, however, in some places, uninjured portions of the or- 

 ganic structure. The main difference between this foraminiferal reef, and more 

 recent coral reefs, seems to be, that while with the latter are usually associated 

 many shells and other organic remains, in the more ancient one the only remains 

 yet found are those of the animal which built the reef" 



The next series of rocks overlying the Laurentian is called the Huronian, 

 which, on the north shore of Lake Huron and to the eastward, consists ofquartz- 

 ites, chloritic slates, liauds of limestone chert, jasper and slate conglomerates, 

 not less than 18,000 feet in thickness. 



On Lake Superior, Sault Ste. Marie, Mamainse, and other places, it is 

 exposed from 10,000 to 16,208 feet in thickness. An approximate estimate of 

 the thickness of this series on Michipicoten Island, says Mr. McFarlane, is 

 18,500 feet. And if we compare the rocks of Michipicoten Island with those of 



