340 F. RUTLEY ON COMMUNITY OF STRUCTURE 
knowledge is acquired, and we can again sail out into the sea of 
legitimate speculation. For this reason I would strongly deprecate 
the abolition of the terms greenstone and aphanite. To uphold the 
old statements with regard to volcanic ash is a much more delicate 
question, since we can, in many cases, prove that these so-called ashes 
may be other rocks, although we are not always in a position to 
prove definitely that they are not ashes. In such instances I would 
earnestly suggest that the terms tuff or breccia be employed, as sig- 
nifying a clastic rock which is not necessarily of pyroclastic origin. 
The older observers deserve all honour for the skill with which they 
frequently detected lithological differences; under similar circum- 
stances few petrologists of the present day could do better; and even 
when the latter have recourse to methods of investigation, formerly 
unknown, they are often compelled to admit the ability with which 
the old work was done, and in many cases the surprisingly acute 
perception of small lithological differences which it evinces. By 
patient study we shall, year by year, get nearer and nearer the truth ; 
but in the present state of our knowledge such an object would be 
considerably retarded if previous experiences were ignored and old 
ideas and old terms ruthlessly abolished. 
It is not quite easy to realize how much we owe to the labours of 
those who have gone before us ; and the least we can do is to recog- 
nize those labours when the results prove to be correct, and to deal 
leniently with errors into which any men might have fallen under 
similar circumstances. The old work ought not to be set aside 
until all facts have been carefully sifted out and preserved ; and it is 
to be hoped that in time some of our pioneers will modify their 
opinions, and thus help their successors in breaking down a few 
of the old-established barriers which for years past have obstructed 
progress, and in building up a stronger and a better belief, com- 
mended by a simplicity of theory and based upon a multiplicity of 
facts. 
Discussion. 
The Presrpent confined his remarks to the question of the 
rounding of grains in stratified rocks. His own experience showed 
that while the larger particles in sandstone rocks are rounded, those 
of smaller size are quite angular. 
Prof. Bonnny, though agreeing with the author as to the great 
difficulty of distinguishing rocks of different modes of origin, was, 
however, inclined to take a more sanguine view, and to hope that 
the experience gained by long and careful study will enable the 
microscopist to discriminate between clastic and pyroclastic rocks. 
He also took exception to the views of the author concerning the 
formation of amygdaloids. 
Dr, Hicks remarked on the suggestiveness of the paper to those 
engaged in the study of the older rocks. He demurred to the 
author’s views as to the deep-sea origin of the Coniston grits. 
