78 Notices of Memoirs — Prof. Lapicorth on the Ordovician. 



I. — Preliminary Note on the Ordovician Kooks of Shropshire. 

 By Professor 0. Lapworth, LL.D., F.G.S. 



[A Paper read before the British Association, Birmingham, Section (C) Geology, 

 September, 1886.] 



IN this note the author gave a orief review of the history of 

 discovery and opinion respecting the Lower Palaeozoic rocks 

 of Wales and the West of England, and pointed out that the results 

 developed of late years by British and foreign geologists made 

 it evident that Murchison's Silurian System, as defined in the later 

 editions of " Siluria," was in reality composed of three distinct 

 geological systems, and that of these three the only one which 

 belonged to him by right of discovery and correct description was 

 the so-called Upper Silurian, which was therefore the only true 

 Silurian System. The lowest known fossiliferous system (the 

 Primordial Silurian of Barrande) was not discovered by Murchison, 

 but by Sedgwick, who regarded it as the lower half of his own 

 Cambrian System, and it ought, as a matter of justice and convenience, 

 to retain that name only. The intermediate system (claimed as 

 Lower Silurian by Murchison, and as Upper Cambrian by Sedgwick) 

 belonged to neither, for its life-types are whollj'^ distinct from those 

 of the true Cambrian below and of the true Silurian above. This 

 distinction must be recognized by a distinct title. The Silurian was 

 named by Murchison after the ancient British tribe of the Silures, 

 who inhabited South Wales, where its rocks attain their fullest 

 development. The rocks of the disputed intermediate system, 

 however, are most fully developed in North Wales — the land of the 

 equally ancient tribe of the Ordovices. The author had proposed in 

 1879 that the middle system should be entitled the Ordovician System, 

 after this old tribe, and this name is gradually coming into use 

 among geologists. 



During the last few years the sequence and fossils of the Ordo- 

 vician strata of Shropshire have been studied in detail by the author, 

 and their igneous rocks, both interbedded and intrusive, have been 

 worked out by Mr. W. Watts. In this note a general summary of 

 his own conclusions was communicated by the author, and illustrated 

 by maps, sections and lists of characteristic fossils. 



Ordovician strata occur in two distinct sub-areas in ShrojDshire, 

 viz. in the district of Shelve and Corndon to the west of the 

 Longmynd, and in the Caradoc district to the east of that range. 

 In both districts these strata are overlain unconformably by the 

 basement beds of the Silurian, loMcJi rest transgressively upon every 

 zone of the Ordovician in turn. 



In the Shelve and Corndon district the Ordovician rocks repose at 

 once upon the highest known strata of the local Cambrian, and are 

 arranged in the following ascending order: — 



