4-6 Mr. Murchison on the Silurian System of Roch. 



that river would have had to force their way; — subsequently, 

 of a portion of the Euphrates finding a partial course to the 

 eastward, through the less obstructed channels of the Tigris, 

 and of the consequently easier and more rapid victory of the 

 sands over the sluggish, and at times almost stagnant waters 

 of the former river; — then of the formation of marshes which 

 would have been alternately flooded and left dry, as the waters 

 of the Euphrates rose and fell ; — till at length the union of 

 the two rivers being perfected, by which completion of the 

 process the united streams would roll together to the ocean, 

 the separate course of the now tributary river, the Euphrates, 

 would gradually become obliterated, and all traces of its ex- 

 istence at length be lost 



When the chorography of the countries in question shall 

 have been investigated with reference to the change above al- 

 luded to, we shall be enabled to understand more fully and 

 more satisfactorily the statements respecting them of the geo- 

 graphers and historians of antiquity: under any other point 

 of view it is an interminable and hopeless task to attempt to 

 reconcile their conflicting, and in many cases apparently totally 

 contradictory, assertions. 

 London, June 1, 1835. CHARLES T. Beke. 



VII. On the Silurian System of Hocks. By Roderick Impey 

 Murchison, F.R.S., Vice-President of the Geological and 

 Royal Geographical Societies, SfC tyc* 

 t^ EOLOGISTS having long felt that the older sedimentary 

 ^-* deposits required a systematic examination, I have de- 

 voted the last five years to the study of this class of rocks, 

 hoping thereby to fill up certain pages which were wanting in 

 the chronology of the sciencef. A table published last year 

 was the first attempt to convey to the geological student a 

 correct view of the thickness, variety of strata, and fossil or- 

 ganic contents of a vast system, which, though arranged by 

 nature in the most lucid order of succession, had not pre- 

 viously been pointed out. These rocks, rising from beneath 

 the old red sandstone in Herefordshire, Shropshire, Radnor- 

 shire, Brecknockshire, Monmouthshire, and Caermarthen- 

 shire, and each distinguished by separate and peculiar organic 

 remains, were respectively named after those localities where 

 each of them could be best studied, and their places in the 

 series most clearly established. I have no change to an- 



* Communicated by the Author. 



f See Lond. and Edinb. Phil. Mag. 1832 to 1835, in the Proceedings 

 of the Geological Society. 



