606 SIR J. W. DAWSON ON BURROWS AND TRACKS OF 



associated with carbonaceous floeculent matter, indicating a horny 

 or membranous sheath. I have long suspected the existence of 

 such tubes, and their connection with many of the cylindrical bodies 

 often confounded with fucoids of the genera PaJmopUycus and 

 ButliotrepJiis^ but have only recently been able actually to demon- 

 strate the fact. 



I'ig. 



10. — AstropolitTion Hindii, a burrow or organism from the 

 Lower Cambrian of Nova Scotia. (' Acad. Geol.' 3rd ed. Suppl. 

 1878, p. 83.) 



In the Black-Eiver Limestone (Trenton group of the Siluro-Cam- 

 brian) at Pointe Claire, on the St. Lawrence, near Montreal, certain 

 layers of grey limestone contain numerous dark-coloured, cylindrical, 

 tortuous bodies, from j-V^h to ^th of an inch in diameter. When 

 broken across, they are seen to be filled with crystalline calcite, as if 

 they had been tubes ; and, when thin slices are prepared for the 

 microscope, the character of their walls, as' composed of fragments of 

 stone and broken shells &c., cemented by an organic material, now 

 carbonised, becomes apparent. Figs. 11 and 12 show the appearance 

 of the tubes on the weathered surfaces, and in section. The species 

 may be thus described : — 



The tubes are 1 to 3 millimetres in external diameter, and 3 

 centimetres or more in length, tortuous, irregular as if sometimes 

 compressed, and sometimes in groups of two or more attached 

 together. This would show a fixed or sessile condition as in 

 Sabellaria or Sabella, rather than freedom, as in the Terehellidce. 



