406 R&R. JI. Murchison on the Silurian Classification. 
that group physically from the upper Silurian, by any line of 
general dislocation. If the lower Silurian rocks in America were 
unconformable to the upper, then it might be contended by those 
geologists who look rather to great physical phenomena than to 
organic life, that the Cambrian was one epoch and the Silurian 
another. But such is not the fact. In North Wales, as in other 
parts of Europe, the upper and lower Silurian fold over in con- 
formable masses, and the lines of dislocation in that broken and 
porphyritic region run at one place through parts of the upper, 
and in others in the inferior fossil beds. There are, it is true, 
certain tracts, particularly that of the Longmynd in Shropshire, 
described by me in the year 1835,* where certain lower Silurian 
strata abut against and repose unconformably on very ancient 
grauwacke, without fossils, and the same may be said of a limited 
tract of inferior grauwacke, near St. Davids. 'To such rocks, 
lying unconformably beneath strata charged with lower Silurian 
fossils, the term Cambrian may be applied, and in the process of 
research some few and, perchance, peculiar organisms may 
found in them. But I distinctly maintain that the so called 
Cambrian never having been characterized by any published fos- 
sils, cannot now be created into a system at the expense of the 
larger part of my well recognized and long established Silurian 
stem, the more so as I am supported by every naturalist who 
has studied the subject, in the opinion that the upper and lower 
Silurian constitute one natural series only. This view is every 
day strengthened by new discoveries. Only a few months ag®, 
I firmly believed, that as no remains of vertebrata had been 
detected in the lower Silurian rocks of any part of the world, 
there was a period when other classes of marine animals abounded 
in the seas, without being accompanied by fishes. But I now 
learn from Prof. E. Forbes, that the defence of an Onchus has 
been found in the lower Silurian rocks, near Bala; whilst it ap- 
pears that Professor Sedgwick and his companions detected last 
summer a similar fragment in true Llandeilo flags. It is therefore 
proved that the same genus Onchus, which Agassiz first descr! 
for me from the fish bed of the Ludlow rocks,+ is now found to 
range down into the lower Silurian; and as rare portions of icb- 
thyolites have also been found in the intermediate strata of Wen- 
lock shale, &c., I willingly correct a generalization which 1 at 
tempted, in declaring my belief that the lower Silurian was 42 
invertebrate period. My eminent friend Agassiz, who is now 
making himself as beloved and admired in the United States, a8 
in Eng and other countries he has visited, has thus in the end 
been borne out by the new discoveries. For, whilst I reasoned 
Ln ERE Pr etc 
* Phil. Mag., June, 1835. 
t See Silurian System, page 256, et seg. 
