Silurian Discussion. 115 



I can make them ; and I am writing from memory, without a 

 single geological work before me, or a single note of reference. 



1. " It is beside the question (he tells me, 4 Literary Gazette? 

 p. 369) to revert to what we respectively did in the field in 1831 

 and 1832." It is not beside the question to have done this. 

 The comparison of our work (at the British Association in 1833) 

 led us, by agreement, to a joint examination of the typical Silurian 

 country in 1834. My friend had most perfect fair play. I did 

 not contest his base line at a single point. On a Silurian ques- 

 tion I believed him infallible ; and I accepted his interpretation 

 of the sections not only in South Wales but also in my own 

 country on the east side of the Berw^yns, where he pronounced the 

 Meifod beds to be his most typical form of Caradoc sandstone, 

 then called Shelly Sandstone. It was not I that cut away the 

 Cambrian rocks from the Silurian. It was he that cut off the so- 

 called Silurian rocks from the general system of North and South 

 Wales, and declared them to form a distinct and superior system ; 

 and as such he described them in his sections, and afterwards 

 coloured them in his map. On no other hypothesis could he give 

 any real meaning to his nomenclature. 



2. In the next paragraph he adds that all the rocks I called 

 Cambrian, and which lay to the west of the Silurian region, were 

 affirmed by myself to be inferior to the strata of his own system. 

 I reply that I cannot consent to have the load of my friend's 

 mistakes thrown upon my shoulders. If there be a single true 

 Silurian rock on the west side of his base line, he has only him- 

 self to blame for the fact ; the mistake is his, and not mine. But 

 taking the Caradoc sandstone as the physical base of the Silurian 

 system, we may still affirm that all the rocks to the west of the 

 true Silurian base are inferior to the whole Siluria7i system. I 

 contend that the Llandeilo flag (which is but one single stage in 

 the Great Bala or Upper Cambrian group) is a Cambrian, and not 

 a Silurian rock. I determined the place of its equivalent (the 

 Bala limestone) correctly in my sections. My friend utterly mis- 

 took the true relations of his Llandeilo flag. Of this I had, as I 

 thought, good evidence in 1846, when I revisited the Silurian 

 country ; and taking the new evidence given by the admirable 

 details of the Government map, we may see at a glance the extent 

 of the mistakes made by him in the interpretation of his Lower 

 Silurian groups. (1.) The want of conformity of the upper to the 

 lower groups is not brought out in the Silurian map ; and this led 

 to a mistaken interpretation of the next inferior group. (2.) The 

 upper part of the Llandeilo group is mistaken for the Caradoc 

 sandstone. (3.) The Llandeilo flagstone is made the base of the 

 system, and is put in every section above the undulatory rocks on 

 its western side. There is not one single section in South Wales 



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