360 Sm WILLIA3I EDMOXD LOGAX. 



gneiss and quartzite and a band of crystalline limestone. This series 

 Logan subsequently showed to be unconformable to the older gneisses, 

 and gave it the name of Upper Laurentian, subsequently exchanged 

 fur that of Labradovian or Norian. 



Indirect evidence that these lowest rocks were not really Azoic was 

 soon pointed out, and in 1858 obscure forms resembling those of 

 Stromatopora were detected in the Laurentian limestones, and were 

 exhibited by Logan to the American Association for the Advancement 

 of Science, in 1859, as probably organic; but it was not till 18C4 that 

 Daw'son announced that these and other similar forms were the remains 

 of a gigantic rhizopod, to which he gave the name of Eozoon Cana- 

 dense. The history of this curious form is well known, and its organic 

 nature, though at one time much contested, is now disputed by few. 



To Logan we owe a large part in the investigations of the Canadian 

 Survey which have established the following great facts in the geology 

 of the Azoic or, as they may henceforth be called, the Eozoic rocks : — 



I. The relations of the Laurentian as a great stratified series of 

 crystalline rocks of aqueous origin, occupying a position at the base of 

 the known geological column and containing evidences of organic life. 



II. The fact of the unconformable superposition to the Laurentian 

 of tlie Upper Laurentian or Norian series. 



II L The firt^t recognition that unconformably overlying the Lauren- 

 tian was still another series of crystalline stratified rocks, the Iluro- 

 nian. (The relative ages of the Norian and Huronian still remain 

 undetermined, for the reason that they have never yet certainly been 

 found in juxtaposition.) 



IV. The fact that the Laurentian, Norian, and Huronian, are all of 

 them unconformably overlaid by the lower members of the New York 

 Paleozoic series. 



His labors on the Laurentian rocks w-ere continued at intervals up 

 to 18G7, and were performed with an amount of fatigue and sacrifice 

 of personal comfort which can only be understood by those who have 

 had to traverse these rugged forest regions. He often wandered for 

 days through a wilderness, with a prismatic conijiass in hand, counting 

 his paces, and gathering rock-specimens as he went. His notes, made 

 in pencil, were always written out each night in ink, and the journey- 

 ings of the day protracted, often by the light of the camp-fire. 



In the iutervals of these investigations, Logan was devoting his 

 attention to another region of crystalline rocks, the extension of the 

 Green Mountains of Vermont through eastern Canada to a point a 

 little south-east of Quebec, the study of which he began in 1847. 



