516 Geological Society: Anniversary Address, 1843. 
lessons, which I first learnt from my friend, were opposed by many 
and accepted by few, though they now form part of the text-book 
of the field surveyor. To a re-examination of this country, then, 
Professor Sedgwick has devoted portions of the two last summers, 
with the distinct object of ascertaining, first, whether he was correct 
in his original opinion, on which I steadily relied, that great masses of 
the slaty rocks of North Wales, sometimes containing fossils, dipped 
under the Silurian rocks described by myself; and if so, secondly, 
what zoological distinction could be established between such rocks 
and those described as Lower Silurian. We were both aware, and 
the point was fully commented upon in my own work, that the Bala 
limestone fossils agreed with the Lower Silurian* ; but depending 
upon his conviction that there were other and inferior masses also fos- 
siliferous, we both clung to the hope that such strata, when thoroughly 
explored, would offer a sufficiency of new forms to characterize an 
inferior system. The results of Professor Sedgwick’s recent re- 
searches would have been communicated to the Society before this 
Anniversary, had not his other avocations prevented his visiting 
London; and as the memoir will shortly be read before you, I will 
now so far allude to it only as to enable us to draw conclusions 
respecting the base of the fossiliferous slaty rocks of North Wales. 
Professor Sedgwick has reassured himself that there are fossili- 
ferous slaty masses, of great vertical thickness, which rise out from 
beneath the lowest Silurian rocks of North Wales hitherto described, 
and occupying the region of Merionethshire and Snowdonia, ulti- 
mately rest upon chloritic and micaceous schists (Menai Straits), 
into which they do not pass. The lowest of these fossil bands, 
forming the summits and flanks of Moel Hebog and Snowdonia, are, 
he conceives, several thousand feet below the Bala limestone. 
The hope, however, which was entertained by my friend, of finding 
these vastly expanded and lower members characterized by pecu- 
liar groups of fossils has been frustrated, and whatever may be the 
thickness of this lowest paleeozoic division, in which he has collected 
a great number of species, he now fully admits, that zoologically it 
is from top to bottom a Lower Silurian series+. Charged as it is with 
characteristic Orthide and Trilobites, including the Asaphus tyran- 
nus, so characteristic of the lowest Silurian rock, there are, as 
might be expected, afew new and undescribed species; and, among 
these, an Ophiura (an animal whose remains had not previously 
been found in strata of higher antiquity than the Lias) will not 
appear the least extraordinary. 
The base of the paleeozoic deposits, as founded on the distine- 
tion of organic remains, may now therefore be considered to be 
firmly established; for the Lower Silurian type is thus shown by 
Professor Sedgwick himself to be the oldest which can be detected 
in North Wales, the country of all others in Europe in which 
there is a great development of the inferior strata. But if classifica- 
tion is settled, there still remains much to be done before North 
* See Silurian System, p. 308. ; 
+ See an expression of the same opinions, Geol. Proc. vol, iii. p. 5. p. 549. 
