178 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 6, 



Having stated that the Upper and Lower Silurian rocks of Europe, 

 including all the fossiliferous strata of Wales, are so knit together 

 by fossils and the transitions of the masses, that they must be viewed 

 as one natural-history series, I will now conclude by simply indicating 

 the small area in various countries to which the Silurian system would 

 be reduced, if the meaning of that term were to be changed and 

 restricted to the upper half of the original system. 



In England, though prominent in the typical districts of Shrop- 

 shire and Herefordshire, the Silurian rocks, so dismembered, would 

 occupy a mere band (scarcely to be defined on a general map) in 

 Brecknockshire, Carmarthenshire and Pembrokeshire; whilst all 

 the broad and specially typical Lower Silurian tracts laid down by 

 me in Salop, Montgomery, Radnor and South Wales must be erased, 

 since it is impossible to distinguish them by their organic remains 

 from the groups of Snowdon. In Ireland, from what we already 

 know, whether through the works of Mr. Griffith, Capt. Portlock, 

 or the labours of the Government Surveyors, the system would pretty 

 nearly disappear, as the great mass of the Irish lower palaeozoic 

 fossils are found to be Lower Silurian. 



In Russia in Europe and in nearly all Scandinavia, Lower Silu- 

 rian rocks and fossils only prevailing, the very name Silurian would 

 be swept from the map, and the system so attenuated would there be 

 confined to Gothland and some small Baltic isles ! 



Now, it must be borne in mind, that even when the lower and 

 upper groups are united in one system as at present, the Silurian 

 rocks of Russia do not occupy one-fifth part of the area of either 

 the Devonian or Carboniferous systems of those regions*, w^hilst in 

 Germany, the whole system, as at present united, bears an infinitely 

 small proportion to the overlying Devonian group. A glance at the 

 Geological Map of America in Mr. Ly ell's work, shows to what a 

 small area, in relation to the other palaeozoic rock systems, the Silu- 

 rian would be reduced, if its lower half were abstracted. 



Independent, therefore, of the impropriety of mutilating a system 

 established on the community of its zoological contents, the results of 

 such an arrangement would be a violation of the meaning which ought 

 in fairness to be attached to a great natural- history period, which was 

 typified as such before the Devonian system was thought of. There 

 are indeed authors who think, that the Upper Silurian is so linked 

 on to the Devonian, that the former, or a large portion of it, might 

 advantageously be merged in the latter ; and if their views prevailed, 

 the only portion of my system or terrain which Professor SedgM'ick's 

 proposition leaves to me would also be swallowed up, and thus, by in- 

 vasions on both sides, the poor Silurian system would be obliterated. 



On the principle however of strata identified by their fossils, geolo- 

 gists I hope agree with me in the conviction in which I abide, that 

 in whatever rocks and to whatever depths the Lower Silurian types 

 extend, the tracts so characterized must be considered to belong to 

 the "Silurian System." 



* See General Map, Russia in Europe and the Ural Mountains. 



