ON A CERTAIN STRUCTURE IN THE LAKELAND 
LAVAS. 
O. KEEGAN, LL.D:; 
Patterdale, Westmorland. 
POO: 
In the discussion which followed the reading of a paper by 
Mr. Ward on ‘ The Comparative Microscopic Structure of some 
Ancient and Modern Volcanic Rocks,’ before the Geological 
Society in 1875, the author, alluding to the decided flow round 
the imbedded fragments which occurs in some of the Lake 
District volcanic ash rocks, observed that ‘this flow was not 
a decided crystalline one, but one merely of chloritic material 
around the larger fragments a 
planes. ’ 
devitrified 1 matter like as in pitchstone, and held that the flow 
Was not due to metamorphism. I have examined several micro- 
sections of volcanic ash of this neighbourhood (Patterdale), and 
1 confess I have never seen therein anything comparable to the 
phenomenon which Mr. Ward has described. e most 
Prominent of these ash-rocks contain very numerous crystals of — 
altered felspar, which are wedged or cemented into the fine 
‘base’ comparatively closely together so as to leave only 
harrow intervals between them, and in these intervals there is 
no specially prominent aspect of anything approaching a flow 
Structure. In the more arenaceous ash deposits, as, e.g., of 
Hall Bank, where the amount of base is considerably greater, 
and ‘the porphyritic ’ constituents are set wide apart, there are_ 
no definite flowing lines distinctly observable. No doubt we 
observe a sort of network of dark brown clots and sprinklings _ 
: ortions of the slide, but these are not 
diffused over some 
formed of chloritic material (more probably they are ferruginous) 
and are not disposed in a regular and orderly manner. a 
_ Everything connected with these ancient rocks is of i impres- 
“Sive interest, but inasmuch as they are clearly much altered and _ 
meta 
es th 
morphosed, the greatest caution is requisite, not only in 
F898 
observa ance of them, but in the. see tis and etereasine a“ : 
fain aags 
