334 THE CANADIAN NATURALIST. [Yol. ix. 



distribution of the strata containing the bedded iron ores, indi- 

 cating approximately the dimensions and direction of the troughs 

 resting on the Cobequid series, and the distribution of those 

 which flank that series on the north-east. More especially these 

 researches have shewn that there are two horizons of iron 

 ore, separated by a considerable thickness of slaty and quartzose 

 strata,^ and underlaid by slate, sandstone, and conglomerate or 

 breccia, difi'ering from those of the Cobequid series. I do not 

 propose here to enter into the details of these observations, but 

 merely to notice their relations to the palaeontology of the district. 



The fossils collected in the district were obviously referable to 

 the " Arisaig series," ranging from the Clinton to the Lower 

 Helderberg inclusive, but the new facts indicated in Mr. Gilpin's 

 manuscript map, which he has kindly communicated to me, 

 suggested more careful local comparisons ; and as my collections, 

 thouo-h extensive, had not been made with reference to the new 

 details of distribution, I thought it desirable to supplement them 

 with additional material. This was obtained by Mr. Donald Fraser 

 of Springville, a well known explorer of these rocks, who by my 

 request visited all the exposures of the iron ores, and collected 

 the fossils found in the ore itself and the including beds, keeping 

 the specimens from each locality separate. In this way a large 

 number of additional specimens were obtained, forming a series 

 of local collections representing the different ore horizons. 



The general result of the study of these specimens is to show 

 that both sets of ore-beds are Upper Silurian, and approximately 

 of Lower Helderberg age. As compared with the typical Arisaig 

 series, as defined in Acadian geology, they represent the middle 

 and upper part of that series. 



The fossils referred to are unfortunately not always in the 

 best state of preservation. They are contained in hard rock, 

 from which they are extracted with difficulty, and are often best 

 studied in the impressions left when they are weathered out. 

 They are also not infrequently distorted. For these reasons it 

 is not always possible to be certain as to their identification ; 

 and in cases of doubt I have given a reference to the known 

 species which they most nearly resemble. 



* In a work on the "Mines and Mineral Lands of Nova Scotia," 

 received while this paper was in the press, Mr. Gilpin estimates the 

 thickness of intervening beds at 700 feet. 



