CURRENT PRE-CAMBRIAN LITERA TURE 425 



The Huronian proper, under whatever local name it may be 

 classed, still remains a readily separable series of rocks. 



The Upper Laurentian, Labradorian, Norian, or anorthosite group 

 is found to consist essentially of intrusive rocks, later in age than the 

 Grenville, but in all probability pre-Paleozoic. 



The general tendencv in our advance in knowledge appears to be 

 in the direction of extending the range of the Paleozoic downward, 

 whether under the old name of Cambrian, or under some other name, 

 applied to a new system defined, or likely to be defined, by a char- 

 acteristic fauna; and under Cambrian, or such new system, if it be 

 admitted, it is altogether probable that the Animikie and Keweenawan 

 rocks must eventually be included. 



The introduction of the term Algonkian, proposed to include the 

 recognizable sedimentary formations below the Olenellus zone, and 

 their igneous equivalents, is believed to be a backward step, for the 

 following reasons: It detaches from the Paleozoic great masses of 

 conformable and fossiliferous strata beneath an arbitrary plane and 

 unites these under a common systematic name with other vast series 

 of rocks, now generally in a crystalline condition; it includes as a 

 mere interlude, what, in the region of the Protaxis, is one of the 

 greatest gaps known to geological history; and it does not in the least 

 degree remove the difficulty found in defining the base of the Gren- 

 ville series. 



Comment. — The statements that there is a general tendency to 

 extend the term Paleozoic downward as our knowledge advances, and 

 that the introduction of the term Algonkian is a backward step, would 

 not be agreed to by the United States geologists. However, this 

 subject is too complex to be discussed in the space at our disposal. 

 Those interested are referred to Bulletin 86 of the U. S. Geol. Survey, 

 and to the Principles of North American pre-Cambrian Geology in the 

 Seventeenth Annual Report of the U. S. Geol. Survey. 



Madison, Wis. C - K - Leith - 



