272 Notices of Memoirs — Sir W. Daivson — Eozoonal Structures, 



refers especially to the typical specimens of Eozoon in which the 

 laminte remain as calcite, while the chambers are filled with 

 serpentine, or more rarely with malacolite, and the canals and 

 tubules with serpentine or dolomite. 



1. As to mode of occurrence and mineral character, in the 

 Vesuvian paper it is wrongly stated that the typical Eozoon is 

 enclosed in a pyroxenic igneous rock. The best specimens have all 

 been found in the thick " Grenville Limestone" of Sir William 

 Logan, estimated by him at 750 feet in its average thickness, though 

 with a few intercalated thin bands of gneiss and quartzite. In the 

 vicinity of Cote St. Pierre in the Seigniory of Petite Nation, where 

 some of the best specimens of Eozoon are found, the outcrop of 

 this limestone has been traced continuously and mapped by the 

 Geological Survey for twenty-five miles, and in the same district it 

 occurs over an extent of more than one hundred miles on the reverse 

 sides of synclinal and anticlinal folds, where it may be recognized 

 by its character and associations as well as by its holding Eozoon. 

 It is true that grains, nodules, and thin interrupted bands of a white 

 variety of pyroxene (malacolite) occur sparingly in this limestone ; 

 but neither in their chemical composition nor in their mode of 

 occurrence have we any proof or even probability of an igneous 

 (intrusive) origin. This was the matured conclusion of the late 

 Dr. Sterry Hunt ; and Dr. F. D. Adams, at present our best authority 

 on these rocks, is of the same opinion. 



The Grenville Limestone has been much bent and folded, and 

 with its accompanying beds has been subjected to regional meta- 

 morphism. In the Petite Nation localities, however, it has not, as 

 far as known, been invaded by igneous dykes or masses. 



Specimens of Eozoon included in this limestone vary from single 

 individuals ranging from an inch to six inches in diameter to 

 aggregated groups of a foot or more; and microscopic examination 

 shows that, in some of the beds in which they occur, there are 

 innumerable fragments showing the same structures scattered on 

 the bed-planes, and associated with the minute globular chamberlets 

 which I have named Archceosphcerince. The specimens of Eozoon 

 may be seen weathered out on the surfaces of the limestone exactly 

 in the manner of Stromatoporse on the surfaces of the calcareous 

 rocks of the Cambrian, Ordovician, and Silurian. 



In certain layers of the Grenville Limestone grains and concretions 

 of serpentine and malacolite occur without Eozoon, and specimens 

 of Eozoon with only so much of such minerals as may be contained 

 in their chambers. There are also instances in which specimens of 

 Eozoon occur attached to or partially imbedded in such nodules, 

 just as Sponges and other organisms occur associated with flints in 

 chalk, or as Stromatoporas occur in connection with concretions of 

 chert in Paleozoic limestones. The origin of the concretions them- 

 selves must have been contemporaneous with the formation of the 

 limestone. 



2. Form and Structure. — An inverted position of Eozoon seems to 

 have been adopted by the authors of the paper and by Zittel. 



