INTRODUCTION. Ixxy 
therefore, that on fossil grounds the whole Bala group was Silurian. Lastly, that he had 
done enough to entitle him to shift his base; to change all his principles of classification ; 
and to absorb all Cambria into Siluria. Such a statement might have seemed compatible 
with literal truth; yet I can hardly think that any English geologist would have accepted 
it as a good ground of classification and nomenclature. 
Geologists, however, did accept the Silurian classification; but on mistaken grounds 
of evidence. A very great and fatal mistake was committed. Who made the mistake ¢ 
In the answer to this question I am at issue with my opponent on a very plain question 
of fact. On this point he has long done me great injustice; which I endured, only because 
I thought it so plain and palpable that it must work its own cure. But I was mistaken; 
for it is greatly aggravated by its mode of insinuation in the words on which I now com- 
ment. I call upon him to do now what he ought to have done long since,—to retract 
a misstatement, on an unequivocal point of fact, which is injurious to myself. I believe that 
he will do so; and so far set himself right. If he refuse to do so, amply and without 
reserve, then I have done with this work of a pitiful controversy: and I have done with 
“ Siluria” now and for ever. : 
Again, he plainly insinuates that I made a mistake in supposing that the old slate- 
rocks of North Wales “were beneath his Lower Silurian types.” I made no such mistake. 
The Llandeilo Flag was his lowest group; and the lowest horizon he can claim for it is 
exactly, or very nearly, that of the Bala limestone. He mistook its relations by placing it 
far above the Bala limestone; and that mistake was exclusively his own. When the mistake 
was corrected, I was ready to admit (under the name Cambro-Silurian) the Caradoc and 
Llandeilo rocks into their true place in the great series of Cambrian rocks. But I will, 
for sake of argument, give up this point, and Silurianize all the Welsh rocks down to the 
Bala limestone. Can my friend then insinuate that [ made a blunder in my descending 
sections, as now given in the Tabular View? Below the Bala limestone I had several 
thousand feet of strata making a very characteristic Lower Bala group; and then, in a 
true descending order, the Arenig porphyries and Festiniog slates; next in order the Lingula 
Flag; then the Harlech grits, and the grand old group of Bangor slates. These collective 
groups were partly fossiliferous, were of enormous thickness, were magnificent as true physical 
groups; and they were all below the Llandeilo group—as that group was understood when 
my opponent (in 1843) took the rash and unwarrantable step of extending his Silurian 
colours over all the old rocks of North and South Wales. 
But in the passage above quoted, my friend has again changed his ground, and 
appealed to a comparatively new interpretation of the Lower Silurian types, and thereby 
greatly mystified his argument. He has deposed the rocks of Llandeilo from their typical 
honours (and indeed it was high time to do so), and now makes the Montgomery sections 
his “prototype.” Technical names may be right or wrong; but they may, if they fail in 
all things else, help us in exposing a fallacy. The flag of Llandeilo was the original type, and 
by the typical relations of that rock were the relations of all other groups of Llandeilo 
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