152 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 25> 



brian series was exactly what it is now. At the end of the summer 

 of 1832 I had made no mistake in 'principle in my interpretation of 

 the phsenomena of North and South Wales, so far as I had studied 

 them ; and most of my best sectional illustrations of the structure 

 of Wales, pubhshed afterwards in successive papers, have been copied, 

 line for line, from sections made in the field during the summers of 

 1831 and 1832. 



§ 4. Historical retrospect of attempts to unite the Cambrian and 

 Silurian rocks in a continuous section. 



In 1834 I studied for the first time the Silurian types under the 

 guidance of my fellow-labourer and friend, the author of the ' Silu- 

 rian System' ; and I was so struck by the clearness of the natural 

 sections and the perfection of his workmanship, that I received, I 

 might say, with implicit faith every thing which he then taught me. 

 We did not, however, discuss or examine together the base-line of his 

 system ; nor did I then, or ever afterwards, comprehend the evidence 

 on which he attempted to define its limits. The whole '* Silurian 

 System " was, by its author, placed, as before stated, ahove the great 

 undulating slate-rocks of South Wales ; although the only sections I 

 had personally examined in 1832 rather seemed to indicate a con- 

 trary position. I knew the labour he had bestowed on his Map, and 

 that he had traced his base-line through a distance (following its 

 sinuosities) of at least 200 miles. Hence, although I saw no good 

 reason, either physical or palseontological, for fixing the base-line of 

 his system exactly where he placed it, I did not at that time enter- 

 tain a thought that he might perhaps have mistaken the geological 

 relations of his lowest groups. 



After making a partition of the country, in which all the forma- 

 tions to the north of Meifod fell to my lot, my fellow-labourer, at 

 my request, made a traverse with me through the undulating cal- 

 careous and fossiliferous rocks between Meifod and Llanrhaidr ; and 

 he identified, without any reserve, the Meifod series with his most typi- 

 cal form of Caradoc sandstone ; and an outlying mass of calcareous 

 slate above Llanrhaidr, he pronounced to be Llandeilo flag. I reluc- 

 tantly accepted these two determinations ; for they involved the upper 

 divisions of my Cambrian sections in most perplexing difficulties, re- 

 specting which I had no misgivings, when in 1833 I explained my 

 sections of the Welsh series to the British Association. 



We then traversed the Berwyn chain to Bala ; and from the top 

 of the pass I explained to him the position of the whole Bala group, 

 extending to the foot of the Great Arenig, the position of the Bala 

 limestone in the group, and the beds over the Bala limestone, which 

 at the south end of the chain were sent off in great undulations, and 

 formed a considerable part of the Upper Cambrian groups of South 

 Wales. 



We then collected fossils from the limestone-quarries near Bala ; 

 and a glance of the eye was enough to show, that, as a group, they 

 nearly agreed with the (so-called) Caradoc fossils of Meifod. Yet 

 such was the conviction produced by the sections from the top of the 



