476 Reviews — The Work of the Geological Survey. 



the Isles of the Sea, form the natural base of this group of strata. 

 These beds contain fragments, many of which are rounded, of the 

 underlying Degnish and Sliuna Limestones. 



In the Eastern Highlands the characters and relative ages of 

 the complex igneous intrusions have been studied, but this subject 

 is still svh jndice. 



Torridonian. — The Torridonian rocks, as they are developed in 

 Eum, have been described by Mr. Harker, who shows that they 

 have been affected by the post-Cambrian thrust-movements. In 

 the north-west of the island a prominent crush-breccia, composed 

 of lenticles of Cambrian limestone and crushed sandstone, overlies 

 the thrust-plane. 



The detailed mapping of the Lower Paleozoic rocks on the north 

 side of the Carboniferous area in South Wales has shown that the 

 anticline in which the oldest rocks come to the surface follows 

 the Towy Valley, and Messrs. Cantrill and Thomas have recognized 

 an inversion which has had the effect of bringing the Didymograptu& 

 hijidus shales over the Llandeilo Beds. 



Old Bed Sandstone and Devonian. — Additional evidence of the fact 

 that the lavas of Lome plateau were poured out on an uneven 

 surface formed of the Highland schists has been obtained in the 

 course of mapping the southern margin of this plateau to the north 

 of Loch Melfort, and definite proof of the Lower Old Eed Sandstone 

 age of the Glencoe volcanic rocks has been furnished by the dis- 

 covery of Psilophyton in shales which are associated with the lavas. 



In England the Old Eed Sandstone rocks on the borders of 

 the South Wales Coalfield have been examined, and evidence of 

 a powerful strike fault, or rather series of faults, traversing the 

 central portion of the northern band has been obtained. " The 

 course of this disturbance," as Mr. Strahan says, " along the middle 

 of the outcrop of the Old Eed Sandstone for so many miles, its effect 

 in throwing in patches of Carboniferous Limestone by what must be 

 an enormous displacement, and lastly, the guiding influence which 

 it has exerted upon the rivers, in common with other disturbances,, 

 of the east-north-east and west-south-west system, all combine to 

 give it an unusual interest." 



In North Cornwall the purple and green slates with Pteraspis- 

 which occur in Watergate Bay have engaged the attention of 

 Mr. Eeid. They are of special interest as indicating, both by their 

 fossil contents and lithological characters, the existence of the Old 

 Eed Sandstone facies within the Devonian area. 



The work of mapping the coalfields of England on the six-inch 

 scale has been continued in South Wales and in the Midland 

 counties, while in Scotland the work of revising the old six-inch 

 maps has commenced. In South Wales the mapping of the coalfield 

 proceeds steadily towards the west, and much information as to the 

 correlation of the coal-seams and the nature of the disturbances will 

 be found in this Summary of Progress. Three systems of faulting 

 or folding exist. The steep uplift which determines the southern 

 margin of the coal-basin ^and the Llanelly syncline belong to the 



