52 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. - 



*' Old Red Sandstone" series of the Welsh area, the lowest or "Tile- 

 stone group," which alone contains the remains of marine forms, has 

 been since very generally referred to the " Upper Ludlow " deposits. 

 The two higher divisions alone represent the typical "Old Red 

 Sandstone;" of these the argillo-calcareous or "Cornstone" group 

 contains just such an assemblage of Fishes as is met with in the 

 palaeozoic fluvio-lacustrine deposits of Scotland ; whilst the upper or 

 "conglomerate and sandstone group," which as yet has only afforded 

 the remains of a HoloptychiuSy includes somewhat abundantly the 

 spoil of a terrestrial surface. On such considerations the "Old Red 

 Sandstone " of Hereford, Monmouth, and Somerset becomes the re- 

 presentative of another freshwater area, the relation and extent of 

 which are indicated in the accompanying Map (PI. I.). Had not 

 the true character of these two peculiar assemblages of depositions 

 been misapprehended, the creation of a "Devonian System" would 

 not have been needed. 



We as yet possess very little detail respecting the so-called " Old 

 Red Sandstone" of the Irish area : from a short communication on 

 the South of that district by Messrs. Jukes and Salter *, we learn 

 that the " Old Red Sandstone " is overlaid by the " Yellow sand- 

 stone " group, and that the two form one continuous series, charac- 

 terized throughout by the remains of a terrestrial vegetation {Knorriat 

 Stigmaria). It is in this series that the large Anodons (Anodon 

 Jukesii, Forbes) occur both on the north near Thomastown and on 

 the south near Cork, together with the remarkable Fern-like plant- 

 remains {Cyclopteris Hibernica, Forbes) ; whilst no marine forms 

 whatever have been met with either in the "Old Red Sandstones," 

 or the " Yellow sandstones." Such being the case, we have satis- 

 factory indications of a third fluvio-lacustrine deposit, of wider di- 

 mensions than those of the Welsh and Scotch areas, but yet hardly 

 equalling in extent the larger members of the great lake group of 

 North America. 



The lacustrine formations of Ireland are everywhere overlaid by a 

 great detrital series of marine origin, and containing the assemblage 

 of carboniferous forms which occur in beds beneath the Mountain 

 Limestone of Pembrokeshire, in the sandstones of IMarwood, and in 

 like sandstones in the Boulonnais f . Messrs. Jukes and Salter 

 notice a very interesting fact with respect to the series above the 

 " yellow sandstone " (which they have termed the " Coomhola 

 grits "), which consists in its unequal thickness from E. to W. ; so 

 that, whilst in the E. it may be taken at from .50 to 60 feet, it has 

 been estimated at 5000 feet in Bantry Bay. We know from this 

 that the depression which brought the marine series over the lacus- 

 trine one was accompanied by a greater amount of depression on the 

 W. than on the E., — a fact which is further supported by other 

 considerations. 



The lacustrine "Old Red Sandstone" of Ireland everywhere over- 



* Meeting of Brit. Assoc. 1855. 



t Quart. Journ. Geol. Soc. vol.ix. p. 23L 



