1865.] DAWSON — STRUCTURE OF EOZOON. 99 



by currents and eddies into rudely parallel and curving layers; the 

 mixture becoming gradually more calcareous as it recedes from the 

 pyroxene. Sometimes beds of limestone of several feet in thick- 

 ness, with the green serpentine more or less aggregated into layers, 

 and studded with isolated lumps of pyroxene, are irregularly in- 

 terstratified in the mass of rock ; and less frequently there are met 

 with lenticular patches of sandstone or granular quartzite, of a 

 foot in thickness and several yards in diameter, holding in abun- 

 dance small disseminated leaves of graphite. 



The general character of the rock connected with the fossil pro- 

 duces the impression that it is a great Foraminiferal reef, in 

 which the pyroxenic masses represent a more ancient portion, 

 which having died, and having become much broken up and 

 worn into cavities and deep recesses, afforded a seat for a new 

 growth of For a mini f era, represented by the calcareo-serpentinous 

 part. This in its turn became broken up, leaving in some places 

 uninjured portions of the general form. The main difference be- 

 tween this Foraminiferal reef and more recent coral-reefs seems to 

 be that, while with the latter are usually associated many shells 

 and other organic remains, in the more ancient one the only 

 remains yet found are those of the animal which built the reef. 



ON CERTAIN ORGANIC REMAINS 

 IN THE LAURENTIAN LIMESTONES OF CANADA .* 



By J. W. Dawson, LL.D., F.R.S., 

 Principal of McGill University, Montreal, Canada. 



At the request of Sir William E. Logan, I have submitted to 

 microscopic examination slices of certain peculiar laminated forms 

 consisting of alternate layers of carbonate of lime and serpentine, 

 or of carbonate of lime and white pyroxene, found in the Lauren- 

 tian limestones of Canada, and regarded by Sir William as possi- 

 bly fossils.f I have also examined slices of a number of lime- 

 stones and serpentines from the Laurentian series, not showing 

 the external forms of these supposed fossils. 



The slices were prepared by the lapidary of the Survey, and 

 were carefully examined under ordinary and polarized light, with 



[* See a preliminary notice in Silliman's Journal [2], xxxvii, 2 72. J 

 f Canadian Naturalist, 1859, p. 300. 



