IS 



was for a moment induced to think, that it Wd\iM 'be better to ttietgt* 

 the two lower formations under one local name ; but the clear sec- 

 tions of South Wales, and those on the eastern flanks of the BerM'yns, 

 where the slaty calcareous rocks with large Asaphi are seen to dip' 

 under great masses of Caradoc sandstone, confirmed me in the re- 

 solution to adhere to the two local names. I trusted that as de^^ 

 tailed surveys were made, the truth of their relations would be 

 confirmed (under those limitations which are common to all depo- 

 sits) : whilst in the tracts where the calcareous matter thins out, 

 and no clear lithological or physical differences exist, I urged 

 that the whole of the inferior type should be distinguished from the 

 Superior by the name of Lower Silurian. I have myself, thereforcj' 

 provided for the cases when the local types are merged ; but I am 

 glad they were proposed, because they have already served as useful 

 horizons for the labours of the Ordnance Geological Suryeyy to 

 which I now call your attention. ..virinMiMr d 



Ordnance Geological Survey of England, — The progress W'hicW' 

 was confidently expected at the hands of the Ordnance Geological; 

 Survey, directed by Sir Henry De la Beche, has recently been so 

 effectively extended to a country with great part of which I am well 

 acquainted, that, whilst we are considering the subject of the Pa- 

 laeozoic Rocks, I take the opportunity to add my tribute to the large 

 share of public approbation which such labours must earn fbr their- 

 authors. If ray few comments on this subject involve reference to 

 my own work, I trust the Society will believe that such allu&ions are 

 made solely to explain the subsequent progress of other geologists. 



In my last Address I alluded to the valuable researches of the 

 Ordnance Geological Survey in South Wales, particularly in the 

 great coal-basin ; and I have now to speak of them amid the older 

 rocks of Pembrokeshire and Caermarthenshire, forming the south- 

 western tracts of the country termed the Silurian region. In the 

 survey of that region, my chief object, as you know, Gentlemen, 

 was simply to ascertain the general classification and right order of 

 certain fossiliferous strata beneath the Old Red Sandstone. Having 

 worked out the succession in typical districts in Shropshire, Here- 

 fordshire, Radnor and Montgomeryshire, I afterwards traced them 

 to the south-west, until I equally determined their relations to the 

 superior deposits in the coast-sections of South Wales. Although 

 the labours in the latter country were thus auxiliary only to those of 

 the arena on which the classification was established, I have had 

 great satisfaction in finding, that my chief boundary lines of Old 

 Red Sandstone and Upper and Lower. Silurian Rocks are pretty' 

 nearly those which have resulted from the very systematic Ordnance- 

 Survey, the first corrected field-sheets of which Sir H. De la Beche 

 has allowed me to view. This observation has reference only, bow-- 

 ever, to the development of what may be called one zone of Silurian 

 rocks, or that to which, as contiguous to the Old Red Sandstone, I' 

 gave my chief attention. Of the existence of true Silurian rock«- 

 to the west and north of a certain line which was set up as a de- 

 scending limit in South Wales, I was, I confess, entirely ignorant. 



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