ANNIVERSARY ADDRESS OF THE PRESIDENT. XXXIX 



sandstone, as then understood, comprised two distinct formations ; 

 that east of Caer Caradoc (Horderly, &c.) being equivalent to the 

 Bala rocks, while the group of May Hill, and probably the Coniston 

 grits of Westmoreland, should be associated with the Wenlock and 

 Ludlow series. 



It became necessary for the officers of the Survey to test these 

 views by an appeal to the county originally described, viz. Shrop- 

 shire. The result of their labours is reported by Mr. Salter and 

 Mr. Aveline, who undertook the task, in the first part of our tenth 

 volume. They have shown that Professor Sedgwick's view is sub- 

 stantially correct, and that the typical district contains not only 

 the equivalents of the Bala and Llandeilo rocks, but also the upper 

 portion of the Caradoc, lying unconformably on the lower, and every- 

 where characterized by the Pentameri, and full of Upper instead of 

 Lower Silurian species. These latter strata are therefore the exact 

 equivalents of the May Hill, &c. beds. But although these rocks 

 are thus evidently brought into a nearer comparison with the ' Clin- 

 ton group' of North xlmerica and with the Pentamerus beds of 

 Russia, they are still regarded by the Government surveyors as 

 forming a bed of passage from the Lower to the Upper Silurians, in- 

 asmuch as several species which characterize the Lower Silurians are 

 common in them, and especially since their distinguishing fossils, 

 the Pentameri and Atrypse, are found in certain portions of the Llan- 

 deilo flags, but are not known to rise into the overlying Wenlock 

 strata. They propose to retain the name of " Caradoc sandstone " 

 for these beds. 



This evidence of intermixture of fossil species has received unex- 

 pected confirmation from America. Li the second part of his ' Palae- 

 ontology of New York,' Professor Hall has announced the fact, that 

 a few of the most characteristic of the fossils of the Trenton lime- 

 stones are now found in the upper part of the Medina sandstone, a 

 formation as intimately connected with the Clinton group, as in our 

 own country the conglomerates that skirt the Longmynds are with 

 the overlying Pentamerus limestones and shales, and the analogy of 

 these beds in the two continents is therefore complete. 



Of the vast thickness and striking geognostic phsenomena of our 

 Lower Silurians, a concise but clear and most interesting statement is 

 presented in Prof. Ramsay's paper " On the Physical Structure and 

 Succession of the Lower Palaeozoics of North Wales and part of Shrop- 

 shire" — the prodromus of a more extensive memoir, new in prepara- 

 tion. These rocks, in the region described, include the prodigious 

 amount of 42,000 feet of apparently conformable strata, including 

 the Cambrian, in the sense in which the term is used on the maps 

 published by the Geological Survey, —the Lingula and Bala series, — 

 and the Caradoc sandstone. The grand facts of Silurian Geology 

 will soon be presented in a complete and consistent picture by Sir 

 Roderick Murchison, whose forthcoming work is anxiously expected, 

 and is sure to fulfil all our anticipations. 



The attention bestowed upon the Older Palaeozoics of England has 

 not of late been extended to the Middle and Upper. Through the 



