THE archean: note II. 191 
the break between the Cambrian and Pebidian was necessarily a 
very great one." 
Professor Lapworth "asked if the name Cambrian was to be 
carried down indefinitely. He had found rocks resembling these 
Pebidian volcanic beds underlying fossiliferous Cambrian strata 
in central England and round the Longmynd." 
Mr. Hudleston " had difficulty in recognizing the supposed 
unconformity between the Cambrian and the Pebidian, and he 
thought that the volcanic series was the natural base of the Cam- 
brian system." At first sight there is an apparent contradiction 
between these remarks and those previously quoted at p. 133. 
This arises from the briefness of the reports. Mr. Hudleston's 
view is that " there can be no question that the volcanic series 
antedates the conglomerate; but it is highly probable that far 
too much importance has been assigned to the physical break, 
which, in areas admittedly volcanic, is only of minor impor- 
tance for purposes of systematic arrangement. Prof. Bonney (Q. 
J. G. S., vol. xxxix., p. 464) refers to the separation of the vol- 
canic beds of Bangor (identified as Pebidian) from the rocks 
underlying them, and also from the Cambrian; " from the latter" 
he says, "we seem justified lithologically and physically in sepa- 
rating these more or less volcanic beds, and in including them for 
convenience in the Pebidian groups of Dr. Hicks; but the interval 
in time need not have been a very enormous one. Below the rhyo- 
lites, as it seems to me, is the great gap in the record." 
From a consideration of the foregoing statements, your reporter 
would ofier the following suggestions concerning the classification 
of the Archean rocks of Britain. 
(i.) Below the Cambrian beds as originally defined by Profes- 
sor Sedgwick, there are a series of beds, chiefly volcanic, which 
have not undergone any very great metamorphic change. These 
may be spoken of as the Pebidian type, being first described by 
Dr. Hicks under that name. As they are by many writers stated 
to be well separated from the overlying Cambrian beds, and as 
they were not included in that system by its founder, they cannot 
justly be included in it, but must be grouped with the Pre-Cam- 
brian rocks. 
(ii.) At the base of these beds occurs the most important break, 
as shown by physical discordance, and change from comparatively 
unaltered to highly metamorphosed rocks. 
