560 THE UPPER SILURIAN. 



and thin-bedded limestone, with fossil shells, and but very little altered, 

 to which we must return in the sequel in a more particular manner. 



The northern boundaiy of the broad band of metamorphic and 

 hypogene rocks, formed by the union of the two promontories already 

 noticed, extends in a westerly direction along the south side of the 

 Pictou Carboniferous district, until it reaches the east side of the East 

 River of Pictou, when it suddenly bends to the south, allowing the 

 Carboniferous strata to extend far up the valley of that river. Here, 

 as at Arisaig, its margin includes fossiliferous slates, among which is 

 a thick bed of iron-ore including fossil shells. With respect to these 

 fossils, I may remark that they are all marine, that they belong to 

 numerous genera and species, and that they are all of distinct species 

 from those of the formations before mentioned, there being a decided 

 break between the fauna of the Upper Silurian and that of the 

 Devonian period, and of course the Carboniferous fauna is still more 

 remote in its characters. 



Both at Arisaig and the East River excellent opportunities are 

 afforded for studying the contrast between the Upper Silurian and the 

 Carboniferous. The collector may, in the shales of Arisaig or the 

 slates of the East River Hills, collect a great number of marine species, 

 some of them in a fine state of preservation, others distorted and partly 

 defaced by the partial alteration of the containing rocks. At both 

 places he can observe that the rocks containing these fossils have been 

 tilted up and hardened before the lowest beds of the Carboniferous 

 system were deposited. At both places he can find in these overlying 

 Carboniferous rocks abundance of fossils, also marine, but entirely dis- 

 tinct from those of the older group. He thus finds that, in passing from 

 one of these formations to the other, he has passed from one great 

 period of the earth's history to a subsequent one, in which no trace 

 remained of the animal population of the former. He has entered, 

 in short, on a new stage of the creative work. 



Immediately on the east of the East River, the metamorphic band 

 is about fifteen miles in breadth, and includes masses and dikes of 

 syenite and greenstone, and beds of quartzite and slate, the latter of 

 very various colour and texture. Beyond the East River, the meta- 

 morphic band again widens ; and between the upper part of the Middle 

 River of Pictou and that of the west branch of the St Mary's River 

 (the point to which we have already traced its southern boundary) 

 it forms a broad and irregular tract of metamorphic country. West- 

 ward of this tract it becomes narrower, and, after extending between 

 the Stewiacke and Salmon Rivers, sinks beneath the Carboniferous 

 beds, while a group of detached masses of igneous and altered rock, 



