THE HISTOEY OF A DISCOVERY. 51 



and the finer parts of the structure have been almost wholly 

 obliterated. But in the other specimens, where the skeleton 

 stiU preserves its calcareous character, the resemblance between 

 the mode of preservation of the ancient Laurentian Foramini- 

 fera, and that of the allied forms in Tertiary and recent de- 

 posits (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 

 conformable lower ones, or to the calcareous zones of the over- 

 lying unconformable 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 Grenville limestone or to one another. The zone 

 of Grenville limestone is in some places about 1500 feet thick, 

 and it appears to be divided 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 lime- 

 stone, 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 irregu- 

 lar masses of white crystalline pyroxene, some of them twenty 

 yards in length by four or five wdde. They appear to be con- 

 fusedly placed one above another, with many ragged interstices, 

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

 cylindrical 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 

 pare 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 followed in difierent spots by parallel, waving, irregularly 

 alternating plates of carbonate of lime and serpentine, which 



