CHAP. XIII 
THE LAKE DISTRICT 
237 
outcrop of the several sheets which have been traced, rather suggest that 
if any one great central volcano existed, its site must lie outside of the 
present volcanic district, or more probably, that many scattered vents threw 
out their lavas and ashes over no very wide area, but near enough to each 
other to allow their ejected materials to meet and mingle. The scene may 
have been rather of the type of the I’hlegrtean fields than of Etna and 
Vesuvius. If this surmise be true, we may expect yet to recognize little 
necks scattered over the volcanic district and marking the positions of some 
of these vanished cones. 
What appears to liave been one of these small vents stands near Grange 
at the mouth of Borrowdale, where I came upon it in 1890. In the little 
Comb -Beck, the Skiddaw Slates are pierced by a mass of extremely coarse 
agglomerate, forming a rudely-circular boss. The slates are greatly disturbed 
along the edges of the boss, so much so, indeed, that it is in some places 
difficult to draw a line between them and the material of the agglomerate. 
That material is made up of angular blocks, varying in size up to three feet 
long, stuck in every position and angle in an intensely-indurated matrix 
formed apparently of comminuted debris like the stones. The blocks con- 
sist of a finely-stratified shale, which is now hardened into a kind of horn- 
stone, with some felsitio fragments. I could see no slags or bombs of any 
kind. There is no trace of cleavage among the lilocks, nor is the matrix 
itself sensibly cleaved. I believe this to be a small volcanic neck and not 
a “ crush-conglomerate.” It has been blown through the Skiddaw Slates, and 
is now filled up with the debris of these slates. Its formation seems to 
have taken place before the cleavage of the strata, and its firm position and 
great induration enabled it to resist the cleavage which has so powerfully 
affected the slates and many members of the volcanic group. 
It was the opinion of my predecessor. Sir Andrew Eamsay, and likewise 
of Mr. Ward, that the Cumbrian volcanic action was mainly subaerial. 
This opinion was founded chiefly on the fact that, save at the bottom and 
top of the series, there is no evidence of any interstratified sediment of non- 
volcanic kind. The absence of such interstratification may undoubtedly 
furnish a presumption in favour of this view, but, of course, it is by no 
means a pi’oof. Better evidence is furnished by the uneonformability already 
mentioned between the Coniston Limestone and the lavas on wliich it lies. 
Besides angular pieces of lava, probably derived from direct volcanic explo- 
sion, this limestone contains fragments of amygdaloidal andesite, and also 
rolled crystals of striated felspar.^ These ingredients seem to indicate that 
some part of the volcanic group was above water when the Coniston Lime- 
stone was deposited. 
The absence of interstratifications of ordinary non-volcanic sediment in 
the Borrowdale group might conceivably arise from the eruptions following 
each other so continuously on the sea-floor, and at so great a distance from 
land that no deposition of sand or mud from the outside could sensibly 
affect the accumulation of volcanic material. Certainly some miles to the 
1 Messrs. Marker and Marr, Quart. Joura. Ceol. Soc. vol. xlvii. (1891), p. 310. 
