Note 114 — Chapter XI · THE CAMBRIAN VOLCANOES OF NORTH WALES, THE MALVERN HILLS AND WARWICKSHIRE

I see no reason to doubt that the less acid igneous fragments were ejected during the closing phases of volcanic action, even though no such rocks have been found at the surface in situ. We must remember how frequently mixtures of acid and basic materials are to be found in the same continuous series of volcanic ejections and even in the same vent, of which illustration will be given in subsequent pages. Nor should we forget what a mere fragment of a volcanic group is exposed at the surface in the Llanberis district. See Professor Bonney and Miss Raisin, op. cit. p. 596, footnote.