316 THE CARBONIFEROUS SYSTEM. 



rocks continue to skirt the older hills as far as the coast of the Gulf 

 of St Lawrence at M'Cara's Brook, near Arisaig, where they rest 

 unconformably on slates belonging to an older formation. The lowest 

 Carboniferous rocks seen here are conglomerates interstratified with 

 beds of amygdaloidal trap, which have flowed over their surfaces as 

 lava currents, just as the trap of the Bay of Fundy has flowed over 

 the red sandstone. Several of these ancient lava streams alternate 

 with beds of conglomerate ; and while their lower parts have by their 

 heat slightly altered the underlying bed, their upper parts, cooled and 

 acted on by the waves, have contributed fragments to the overlying 

 conglomerate. Over these conglomerates is a great series of reddish 

 and gray sandstones and shales, similar to those we have observed 

 elsewhere. They contain no gypsum, but there is a thick limestone 

 with a number of the fossil shells already noticed in similar beds of 

 this age. Along the whole southern edge of the Pictou district, 

 therefore, we observe the Lower Carboniferous series, distinguished by 

 its characteristic fossils, and containing beds of limestone and gypsum, 

 though the latter, as well as the associated marly beds, is less import- 

 ant than in Hants County. To the northward of these older members 

 of the system, we find in some localities, and especially on the East 

 River, a large development of the productive or Middle Coal measures ; 

 and the remaining part of the district, stretching along the coast of 

 Northumberland Strait, and connected with the eastern part of Cum- 

 berland, presents precisely the same characters which we have observed 

 in the last-mentioned district, of which it is strictly a continuation. 



The most remarkable feature in the Pictou district is the enonnous 

 thickness of Coal measures on the East River, forming the Albion 

 Mines Coal-field ; and these deserve a detailed notice, not only from 

 their economical importance, but their geological interest, as presenting 

 a vastly greater development of coal seams and their accompaniments 

 than we have observed elsewhere. I shall therefore describe the 

 genei'al arrangement of the rocks on the East River with the aid of 

 the sections (Figs. 134 and 136). 



The oldest Carboniferous bed that I have observed on the East 

 River is a limestone resting directly on the edges of a hard meta- 

 morphic slate, which must have formed the sea-bottom on which 

 the former rock was deposited. Angular fragments of the slate are 

 included in the lower part of the limestone. This limestone, which 

 appears at Lime Brook on the east branch of the East River, contains in 

 its upper part fossil corals of the genus Lithostr^otion, already described 

 as L. Pictoense. On this limestone rest marls with gypsum veins, and 

 at least one large bed of gypsum and anhydrite, the outcrop of which 



