142 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



of the volcanic district consists of pyroclastic materials. When my 

 lamented friend, the late Mr. Ward, was engaged in mapping the 

 northern part of the district, which he did with so much enthusiasm, 

 I had an opportunity of going over some of the ground with him, 

 and of learning from him his ideas as to the nature and distribution 

 of the roclvs and the general structure of the region. I remember 

 the difficulty I had in recognizing as tuif much of what he had 

 mapped as such, and I felt that had I been myself required, 

 without his experience of the ground, to map the rocks, I should 

 probably have greatly enlarged the area coloured as lava, with a 

 corresponding reduction of that coloured as tuff. A recent visit to 

 the district has revived these doubts. It is quite true, as Mr. Ward 

 maintains, that where the finer-grained tuffs have undergone some 

 degree of metamorphism, they can hardly, by any test in the field, 

 be distinguished from compact lavas. He was himself quite aware 

 of the objections that might be made to his mapping *, but the 

 conclusions he reached had been deduced only after years of un- 

 remitting study in the field and with the microscope and in the 

 light of experience gained in other volcanic regions. Nevertheless 

 I think that he has somewhat exaggerated the amount of fragmental 

 material in the northern part of the Lake District, and that the 

 mapping, so consistently and ably carried out by him and followed 

 by those members of the Survey who mapped the rest of the ground, 

 led to similar overrepresentation there. Some portions of the so- 

 called tuffs of the Keswick region are undoubtedly andesites ; 

 other parts in.the southern tracts include intercalated bands of felsite 

 as well as andesite. 



But even with this limitation, the pyroclastic material in the 

 Lake District is undoubtedly very great in amount. It varies in 

 texture from coarse breccia or agglomerate, with blocks measuring 

 several yards across, to the most impalpable compacted volcanic 

 dust. In the lower parts of the group some of the tuffs abound in 

 blocks and chips of Skiddaw Slate. Some good examples of this 

 kind may be seen in Borrowdale, below Falcon Crag and at the Quay- 

 foot quarries. W^here the tufi" is largely made up of fragments of 

 dark blue slate, it much resembles the slate-tufis of Cader Idris. 



* He says : — ' I snail be very much surprised if my mapping of many parts 

 of the district be not severely criticised and found fault witli by those who 

 examine only one small area and do not take into consideration all the facts 

 gathered together, during tlie course of several years, from every mountain 

 flank and summit,' Op. cit. p. 25. 



