62 
land, Professor Sedgwick has answered this appeal himself*.' Re- 
éxamining all the ancient fossiliferous rocks iti Cumberland, he has 
become convinced that they are there divisible into two great zones, 
referable to Upper and Lower Silurian types, the former surmounted 
by old réd sandstone and carboniferous limestone, and the latter re- 
posing on some of the oldest sedimentary rocks of our islands, the 
Skiddaw slates; in which no organic remains have been detected. 
Numerous fossils from the Berwyn mountains, Snowdonia, and other 
Cambrian tracts, which he colleeted many” years ago (but which, 
owing to the want of space at Cambridge, have been only lately 
unpacked), have been recently subjected to the same interrogatory; 
and have given the reply, that vast as the thickness of strata may 
be, the same forms of Orthis which typify the Lower Silurian rocks; 
not only range through what had been termed the Upper Cambrian 
(Bala, Berwyns; &c.), but also throughout the: whole of North 
Wales. 
In the mean time other observers had been working out detailed 
facts which pointed to the seme conclusions. “In a part of Cumber- 
land, Mr. James Marshall had established the presence of Silurian 
deposits, where it was formerly supposed still older rocks prevailed, 
and more recently Mr. MacLauechlan of the Ordnance Survey, has 
shown us that all the slaty, and im parts metamorphic tracts of Nortli 
Pembroke; which are coloured in my Silurian map as Cambrian, or 
im other words, as strata beneath the Llandeilo flags, contain many 
of the same forms as the Lower Silurian rocks. Before these inquiries 
had taken place at home, the researches of Professor Sedgwick and 
myself in Germany and Belgium, and of M. de Verneuil and myself 
in Russia, had led to the same conclusions, viz. that wherever it 
exists, the zone of fossiliferous strata characterized by the Lower 
Silurian Orthide, are the oldest beds in which organie life has been 
deteeted, and that many of the subjacent rocks, sometimes even when 
in the form of gneiss, mica schist, tale schist, chlorite slate, &é. aré 
nothing but metamorphic rocks, in less altered parts of which the 
same typical fossils are observable. 
If then our researches teach us that the term Cambrian must 
cease to be used in zoological classification, it being in that sense 
synonymous with “Lower Silurian,” we'see the true value of having 
established a type like the latter, whieh being linked on through in- 
termediary groups to overlying formations, the age of which was 
previously well known, we have arrived gradatim, and without hypo- 
thesis, at the apparently true base of the zoological series in Europe. 
It is right, therefore, that I should announce that the conventional 
line which was set up in the map of the Silurian region, between the 
Lower Silurian and the Cambrian rocks, and which has been adopted 
by Mr. Greenough, has no longer any reference to strata identified 
by distinguishing organie remains, for the same fossils are found in 
strata on each side of that demarcation. Such lines of division, 
however, when viewed as the signs of local phenomena, are not- 
* Proceedings, No. 82, p. 541. fy 53h 
