c 



I 



98 THE CANADIAN NATURALIST. [April 



aminifera and that of the allied forms in Tertiary and recent 

 deposits (which, as Ehrenberg, Bailey, and Pourtales have shown, 

 are injected with glauconite), is obvious. 



The Grenville specimens belong to the highest of the three 

 already mentioned zones of Laurentian limestone, and it has not 

 yet been ascertained whether the fossil extends to the two confor- 

 mable lower ones, or to the calcareous zones of the overlying un- 

 conformable Upper Laurentian series. It has not yet either been 

 determined what relation the strata from which the Burgess and 

 Grand Calumet specimens have been obtained bear to the Gren- 

 ville limestone or to one another. The zone of Grenville limestone 

 is in some places about 1500 feet thick, and it appears to be divi- 

 ded for considerable distances into two or three parts by very thick 

 bands of gneiss. One of these occupies a position towards the 

 lower part of the limestone, and may have a volume of between 

 100 and 200 feet. It is at the base of the limestone that the fossil 

 occurs. This part of the zone is largely composed of great and 

 small irregular masses of white crystalline pyroxene, some of them 

 twenty yards in length by four or five wide. They appear to be 

 confusedly placed one above another, with many ragged interstices, 

 and smoothly-worn, rounded large and small pits and sub-cylindri- 

 cal cavities, some of them pretty deep. The pyroxene, though it 

 appears compact, presents a multitude of small spaces consisting of 

 carbonate of lime, and many of these show minute structures similar 

 to that of the fossil. These masses of pyroxene may characterize a 

 thickness of about 200 feet, and the interspaces among them are filled 

 with a mixture of serpentine and carbonate of lime. In general a 

 sheet of pure dark green serpentine invests each mass of pyroxene ; 

 the thickness of the serpentine, varying from the sixteenth of an 

 inch to several inches, rarely exceeding half a foot. This is fol- 

 lowed in different spots by parallel, waving, irregularly alternating 

 plates of carbonate of lime and serpentine, which become gradually 

 finer as they recede from the pyroxene, and occasionally occupy a 

 total thickness of five or six inches. These portions constitute the 

 unbroken fossil, which may sometimes spread over an area of 

 about a square foot, or perhaps more. Other parts, immediately 

 on the outside of the sheet of serpentine, are occupied with about 

 the same thickness of what appear to be the ruins of the fossil, 

 broken up into a more or less granular mixture of calc-spar and 

 serpentine, the former still showing minute structure ; and on the 

 outside of the whole a similar mixture appears to have been swept 



