662 EEPORT— 1886. 



ouglit, as a matter of justice and convenience, to retain that name only. The inter- 

 mediate system (claimed as Lower iSilurian by jMurcliison, and as Upper Cambrian 

 by Sedgwick) belonged to neither, for its life-types are wholly distinct from those 

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

 be recognised by a distinct title. The Silurian was named by Murchison after the 

 ancient British tribe of the Silm-es, who inhabited South Wales and Central Shrop- 

 shire, 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 this middle system should be entitled the Ordovician System, after this old 

 tribe, and the name is gradually coming into use among geologists. 



During the last few years the sequence and fossils of the Ordovician 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. 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 districts in Shropshire, 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 imcouformably 

 by the basement beds of the Silurian, which rest trau.sgressively upon every zone 

 of the Ordovician i]i 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 foUowiDg 

 (ascending) order : — • 



Shelve Seeies — 



(«) Stiper Groiij), consisting of tlie well-known Stiper quartzites and their 

 associated strata. 



(6) Ladyivell Group, composed of the dark shales and flagstones of Mytton, 

 Ladywell, and Hyssington, with Dk-Jwyi-frptida and Otjyyia Selwynii, Sec. 



(c) Stapeley Volcanic Group — Andesitic lavas, ashes, and interbedded shales. 

 Meadowtown Sekies — 



(a) Weston Group of Grits, flagstones, and dark .shales. 



(b) Middleton Group, composed of dark shales with Didy. Murchisoni, and cal- 

 careous flagstones with Oyyyia Buchii and Ascipkus tyrannus. 



(e) Sorrinyton Group of intensely black shales with Ccmoyrdptus and Lepto- 

 graptus. 



Chirbtjet Seeies — 



(«) Aldress Group, composed of the Spy If'ood calcareous yrit, and the Aldress 

 Graptolithic shale. 



(h) Marrinyton Group, including the Hayley volcanic ashes and shales, and the 

 Whittery ashes and overlying shales. 



The only Ordovician roclis occurring east of the Longmynd are those forming 

 the local Caradoc Series of the author (the Caradoc formation of geologists). The 

 basement beds of this series rest unconformably upon all the older rocks of the district 

 - -upon the so-called Uriconian, Longmyndian, Wrekin quartzite, and Shineton shales 

 — and its component zones are each covered up unconformably in turn by the 

 basement beds of the Silurian. This isolated Ordovician series is composed of the 

 following members : — 



C.VR.iDoc Series — 



(a) Hoar lidye conglomerate, grits, and limestone. 



(6) Harnaye Shales. 



(e) Cliatuall Sandstone. 



(d) Lonydlle Flays. 



(e) Onny, or Trinucleus Shales. 



The Shelve series answers generally io the strata commonly designated Arenig; 

 the Meadowtown series includes the typical members of Murchison's Llandeilo; and 

 the Chirburv and Caradoc series correspond broadly to Sedgwick's Bala formation 

 of North Wales. 



Some of the most characteristic fossils of each of the Ordovician subformations 



