1XX1V PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I906, 



The Falcon-Crag Group, 1 so far as I know, only occurs in force 

 in a roughly-triangular tract lying east of Derwentwater, between 

 that lake and the Thirlmere Valley. The rocks consist usually of 

 rather thin, often vesicular, lavas alternating with ashes ; but a few 

 more massive lavas also occur, as well as some thick accumulations 

 of coarse breccia. 



The Ullswater Basic Group is more widely spread, forming a 

 very irregular semi-ellipse on the east, north, and west of the 

 Scawfell Ashes of the central group of fells. The lavas are, on 

 the whole, more massive than those of the underlying Falcon-Crag 

 Group, otherwise there is little difference between the rocks of the 

 two groups. The reasons for our identification of the well-known 

 rocks of Eycott Hill with this group are given in brief in the 

 i Notes ' already cited. 



The Sty-Head Group has a more restricted distribution, being 

 found chiefly on the north and west, and in a smaller degree on the 

 south of the Scawfell cluster of fells. The rocks, consisting of 

 lavas, ashes, and breccias, are marked by their massive character, 

 although this is no doubt largely due to their subsequent alteration. 



The succeeding group occurs in two forms, owing to difference 

 in the type of alteration which they have subsequently undergone. 

 They are essentially pyroclastic, lavas being so scarce that they 

 may here be ignored, and the rocks consist of alternations of finely- 

 laminated volcanic dust and coarser breccias. In the central fells 

 of the Scawfell group, and to a less degree elsewhere, they have 

 been changed into rocks which may be described as horns tones; 

 while, in the band which runs from Coniston to the neighbourhood 

 of Shap, they are well cleaved, and give rise to roofing-slates. 



The Shap Andesites are chiefly thin vesicular lavas, interbedded 

 with ashes, and call for no further notice. 



The Shap Rhyolites, again, are of little importance to the present 

 subject, save in the neighbourhood of Coniston, where a massive 



misled by the occurrence of some undoubtedly-intrusive rocks of the same 

 general characters in Borrowdale. My colleague Mr. Harker was, I believe, 

 always of the opinion that they were contemporaneous; and the contem- 

 poraneous date of the great mass of the rocks lying below the Scawfell Ash- 

 Group has been established beyond doubt by the late E. E. Walker, in his paper 

 ' On the Garnet-bearing & Associated Rocks of the Borrowdale Volcanic Series ' 

 (Quart. Journ. Geol. Soc. vol. Ix, 1904, p. 70). 



1 A provisional map of the volcanic rocks of the district, by Mr. Harker 

 and myself, will be found appended to the report of the Long Excursion to 

 Keswick, Proc. Geol. Assoc, vol. xvi (1900) pi. xiii, facing p. 526. 



