40 ^^T^paoeEEDINGS OP THE GEOLOGICAL SOCIETY* [June 3- 



If on th§ contrary, we continue to unite the Ludlow and Wenlock 

 as originally proposed, by calling it Upper Silurian, we have a group, 

 \Yhich, however the fossils of its lowest part or the Wenlock shale 

 occasionally graduate into the subjacent strata, is, on the whole, as 

 clearly separated from that beneath it (whether in the Siluria of the 

 British Isles, the continent of Northern Europe, or in North America) 

 as any two groups belonging to the same series which geologists 

 have attempted to define in rocks of secondary or tertiary age. 



It has been stated by Professor Sedgwick, that " beautiful as the 

 sequence of Siluria is, it is not the true mineral type, either for En- 

 gland, Wales or Ireland." Let me here say that I never proposed it as 

 a general mineral type, but simply as a good fossiliferous type of rocks 

 of that age. Few persons, on the contrary, could I think have laboured 

 harder than I myself did to afford evidence of the great lithological 

 differences which are observable even within the Silurian region, by 

 the comparisons I then instituted between the slaty Silurian groups 

 of West Shropshire, Montgomery, Brecon, Caermarthen and Pem- 

 broke, and their calcareous equivalents in other parts of Shropshire, 

 and in Radnorshire, Herefordshire, &c. But what I did contend for, 

 and what I think European and American researches have con- 

 firmed, was, that in selecting as types those tracts, which, void of 

 contemporaneous igneous rocks and slaty cleavage, were full of cal- 

 careous matter, and consequently of fossils, and in running them out 

 into countries where such calcareous matter thinned out, and with it 

 many of the fossils, and where strata precisely of the same age assumed 

 a slaty cleavage, and were associated with igneous rocks, I enabled 

 others who might follow me to estimate mineral conditions attheirtrue 

 value. 



Whilst I thus indicated to geologists who might explore those 

 tracts in which strata of like age occurred, that they must not ex- 

 pect to find elsewhere Aymestry, Wenlock, Woolhope and Llandeilo 

 limestones exactly in the order in which they occurred in my typical 

 districts, I stated emphatically, that what I expected to result from 

 extended inquiries in Europe, would be the confirmation of the 

 existence of two united natural groups ; the quantity, variety and 

 identity of species in each being regulated by the varied mineral 

 character or conditions of the deposits in the different countries 

 appealed to. This appeal having now been made, my surprise 

 is, first, that notwithstanding numerous diversities in lithological 

 structure, so many typical forms should appear in synchronous 

 palaeozoic strata in very distant kingdoms ; and secondly, that 

 there should even be, as far as Europe is concerned, such 

 occasional striking coincidences of mineral succession ; — in a word, 

 that flaggy and thin-bedded limestones should appear at great 

 distances from England on the horizon of the Ludlow rocks, — that 



system, and I then obseiTed to Mr. Marshall, who accompanied me from Coniston 

 to Ulverstone, that there could be no sort of doubt that the Coniston limestone 

 represented a part of the Lower Silurian, whilst on the whole the Kendal and 

 overlying schistose series represented the Upper Silurian group. In fact, I urged 

 Mr. James Marshall to publish a memoir on his Coniston band. 



