Vol. 58.] | AND ASSOCIATED BEDS OF THE MALVERN HILLS. 149 
graptolithologists ‘await with keen interest the results of Holm’s 
revision of Kichwald’s typical Dictyonema flabelliforme, so that they 
may separate out satisfactorily the various forms which, on both 
sides of the Atlantic, have hitherto been provisionally grouped under 
that name and that of Dictyonema sociale. So gradually do the 
typical Cambrian and Ordovician faunas shade one into the other in 
most regions, and so convenient is it for mapping purposes to select. 
a lithological break as the dividing-line, that it will probably be 
found that for some years to come we must content ourselves in 
many districts with drawing an approximate boundary-line between 
the two. 
Mr. Puitie Laxe remarked that the trilobites which had been 
found in the White-Leaved-Oak Shales belonged to the Upper 
LInngula-Flags ; but it appeared from the Author’s correlation with 
the Warwickshire sequence, that the Lower Lingula-Flags might 
also be represented. There seemed, however, to be an entire 
absence of Middle Lingula-Flag forms ; and he asked whether this 
apparent absence was due to an unconformity, or to a fault, or 
merely to the fact that no fossils had yet been found in the inter- 
vening beds. 
With regard to the limits of the Cambrian and the Ordovician, the 
Tremadoc Slates were undoubtedly passage-beds, and the selection 
of any particular horizon as the boundary was largely a matter of 
convenience. Palzontologically, at least so far as the trilobites 
are concerned, the Tremadoc Series, as a whole, appears to be more 
closely related to the Ordovician than to the Cambrian. 
The AvrHor said that he was glad that his work had led him to 
conclusions so closelyin agreement with the views of Prof. Lapworth. 
With reference to the term ‘Olenellus-zone, he might say that 
it had been used in a wide sense employed by many geologists. He 
added that since the similarity of the names ‘ Hollybush Sandstone’ 
and ‘ Hollybush Quartzite’ might lead to confusion, he was quite 
prepared to adopt Prof. Lapworth’s suggestion, and proposed to 
employ a new term in place of the latter. He had not entered 
into the specific differences between the Dictyonemas of the Dictyo- 
nema-shales, but had simply regarded them either as forming or as 
not forming a definite zone, which might be simple in character, or 
complex like that of Spheerophthalmus. 
In reply to Mr. Lake, he said that beds representing the Middle 
Lingula-Flags might be present, though concealed, in the Malvern 
district. 
