18 



ME. G. W. LAMPLEGH ON SOME EFFECTS OP [Feb. I9OO, 



distinguishing between original and superinduced features in rocks 

 of this character, I am inclined to regard this agglomerate as 



derived, at least in part, 

 from the disruption of 

 portions of the adjacent 

 basalt during the move- 

 ments. Some degree of 

 smashing must certain- 

 ly have taken place in 

 these basalts. Thus at 

 Cromwell's Walk the 

 dyke-like mass, 15 to 

 20 feet thick, has had 

 a segment sliced off and 

 thrust forward among 

 the agglomerate so that 

 the beautifully distinct 

 flow-lines of vesicles are 

 sharply truncated along 

 the fractured edge, 1 and 

 the same edge displays 

 a succession of gaps and 

 notches, now filled in 

 with the enveloping ash, 

 from which blocks have 

 evidently been broken 

 and presumably are 

 now to be found in the 

 adjacent agglomerate. 

 Fractures of the same 

 kind are sometimes 

 found to cut up the 

 thinner bands of basalt 

 in such a manner that 

 Z Jo "Sd£ it is impossible to fix 

 the point where the 

 lava ends and the agglo- 

 merate begins. More- 

 over, the agglomerate is 

 full of limestone-blocks 

 in the vicinity of the 

 included strips of lime- 

 stone, and of vesicular 

 basalt in the neigh- 

 bourhood of the basalt- 

 masses ; and though the 

 two kinds of blocks are 

 also commingled, their 





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1 As described and figured by Sir Archibald Geikie in his ' Ancient Volcanoes 

 of Great Britain ' vol. ii (1897) p. 31. 



