190 REPORT OF THE AMERICAN COMMITTEE. 
the rock in the field, we can have no doubt of its sedimentary 
origin, bedding being often well-marked and foliation distinct, 
yet, under the microscope, it is extremely difficult to identify any 
of the constituents, in their present condition, as of clastic origin 
... of this stage of metamorphism, which, so far as we can 
tell, is as complete as can be. The rocks of the southern face of 
Ben Fyn furnish excellent examples. In England I may cite as 
instances the schists of the Lizard peninsula, and a considerable 
number of those in Anglesey, though some which have been sent 
to me from that island belong rather to the former type. 
"Between these types, intermediate instances will, of course, be 
found. The third type, while agreeing with those described 
under the second head as being metamorphosed to the highest 
degree, appears to differ in respects which can hardly be due to a 
mere prolongation of the metamorphic action. The bedding of 
these rocks is ill-marked ; they are coarsely crystalline and often 
granitoid in aspect, being then difficult to distinguish from rocks 
of igneous origin, and the same is true of their microscopic 
structures. In such cases, in the present state of our knowledge 
(though I do not think it will be so always), we must be content 
to be sometimes uncertain whether we have before us a granite or 
a gneiss. Examples of this class are the coarse gneisses of the 
Hebridian series, which underlie the Torridon sandstone and 
many of the Malvernian rocks of England, At the same time 
it must be remembered that now and then beds more distinctly 
foliated also occur in this series. 
"Naturally we should expect that, as a rule, the above distinc- 
tions should have a certain chronological value, and thus we are 
justified in using them in default of other evidence and with due 
caution for purposes of classification." 
In a paper (Q. J. G. S., vol. xxxix., p. 261) "On the supposed 
Pre-Cambrian rocks of St. David's," by Dr. A. Geikie, the author 
denies the existence of any such rocks in the St. David's area. In 
the discussion which followed this paper. Prof. Bonney remarked, 
"As regards the separation of the Pebidian from the Cambrian, 
to himself there appeared to be an unconformity at the base of 
the quartz-conglomerate, certainly there was an entire change in 
the lithological character of the deposits. The conglomerate in- 
troduced a series of beds different in aspect, color, materials, 
and conditions. He did not say, and never had thought, that 
