608 PEOCEEDINGS OF THE GEOLOGHCAL SOCIETY. [June 20, 



The Haversian system is in direct communication with the surface, 

 giving rise to the wide pores. Sections of Rhomhoptycldus show the 

 same structure, as do those of Rliizodopsis (H. sauroides) in Wil- 

 liamson's memoir. The absence of ganoin is therefore not the re- 

 sult of accident, but is due to the same cause in Megalichthys as in 

 the other two genera named — non-development. 



Though the main facts regarding these genera are sufficiently well 

 ascertained, much still remains to be done in the working out of 

 their details. The statements I have made will, in all probability, 

 require modification and correction as better-preserved specimens 

 turn up. 



Prom comparison of a large suite of specimens it appears that, while 

 the typical scales of Megalichthys and Bhomboptychius are sufficiently 

 distinct, the examples are very many which may, in the absence of 

 other proof, be referred to either genus. Great differences of the 

 scales of the same individual might account for the apparent confu- 

 sion ; but no specimens have been found sufficiently complete to make 

 this certain. 



13. Note on supposed Burkows o/Woems in the Laurentian Hocks 

 of Canada. By J. W. Dawsoit, LL.D., P.R.S., F.G.S., Principal 

 of M'Gill University, Montreal. 



Among other indications of fossils in the Laurentian rocks, men- 

 tioned in my paper on the structure of Eozoon*. are certain per- 

 forations resembling burrows of worms, found in a calcareous 

 quartzite or impure limestone from Madoc, in Upper Canada. They 

 occur in specimens in the Museum of the Geological Survey, and 

 also in specimens subsequently collected by myself at the same 

 place. 



The beds at Madoc, containing these impressions, underlie, un- 

 conformably, the Lower Silurian limestones, and are regarded by 

 Sir W. E. Logan as belonging to a somewhat higher horizon in the 

 Laurentian than the Eozoon Serpentines of Grenville. They are also 

 less highly metamorphosed than the Laurentian rocks generally. 

 They are described in Sir W. E. Logan's Eeport on the Geology of 

 Canada, 1863, at p. 32. 



The impressions referred to consist of perforations approaching to 

 a cylindrical form, and filled with rounded siliceous sand, more or 

 less stained with carbonaceous and ferruginous matter, more espe- 

 cially near the circumference of the cylinders. These superficial 

 portions being harder than the containing rock, and of darker colour, 

 and also harder than the interior of the cyhnders, project as black 

 rings from the weathered surfaces ; but in their continuation into 

 the interior of the mass, they appear only as spots or lines of a 

 slightly darker colour, or stained with iron-rust. 



When sliced transversely and examined under the microscope, 

 they appear as round, oval, or semicircular holes drilled through the 



* Quart. Journ. Geol. Soe, Feb. 1866. 



