MINERALS AND GEOLOGY OF CANADA. 197 
terms Bird’s Eye and Black River Limestone, or the latter alone, 
is occasionally employed in reference to the beds in question: thus 
partially recognising two sub-formations, the Bird’s Eye and Black 
River (united) below, and the Trenton proper, above. The strata of 
the entire group average from 600 to 700 feet, and consist almcst 
wholly of limestones, usually of a grey or black colour, and more 
or less bituminous. Here and there.a bed of sandstone, rarely ex- 
ceeding two or three feet in thickness, and a thin seam of calcareous 
clay, may occur amongst the series; but limestone rocks essentially 
characterize the formation. Some of these are thick, and others thin- 
bedded, the latter passing into limestone shales. Fossils are exceed- 
ingly abundant in most of these beds. Those more especially charac- 
teristic of the lower sub-division, comprise :—Tetradium fibratum 
(fig. 167), Columnaria alveolata (fig. 168), Stromatopora rugosa 
Fig. 167.—Tetradium fibratum Fig. 168. — Columnarta 
(Safford). alveolata (Goldfuss). 
Fig. 169.—Stromatopora 
rugosa (Hall). 
Fig. 170.—Maclurea Logant (Hall). 
