176 J. D. Dana — Sedgwick and Murchison. 



wick uses the term Carribro-Silurian to include, beginning 

 below, (1) " Conglomerates and slates, (2) Lower Llandeilo flags, 



(3) Slates and grits (Caradoc Sandstone of Noeth Grug, etc., 



(4) Upper Llandeilo flag passing by insensible gradations into 

 Wenlock shale." The Cambrian series is made to include (I) 

 The Festiniog or Tremadoc group ; (2) Roofing slates, etc., the 

 " Snowdonian group," fossiliferous in Snowdon, etc. ; (3) the 

 Bala group ; and then (4) " the Camhro-Silurian group," com- 

 prising u the lower fossiliferous rocks east of the Berwyns be- 

 tween the Dee and the Severn — the Caradoc Sandstone of the 

 typical country of Siluria— and the Llandeilo flags of South 

 Wales, along with certain associated slates, flags, and grits." 

 The extension of the term Silurian down to the Lingula flags, 

 or beyond, is opposed because the beds below the Llandeilo are 

 not part of the Silurian system ; the term Silurian [derived 

 from the Silures of Southeast Wales and the adjoining part of 

 England] is not geographically applicable to the Cambrian 

 rocks ; and because the only beds in North Wales closely com- 

 parable " with the Llandeilo flags are at the top of the whole 

 Cambrian series." This last reason later lost its value when 

 it was proved, as Sedgwick recognized years afterward, that 

 Murchison's Llandeilo flags were really older than Sedgwick's 

 Bala rocks. 



Sedgwick's paper was followed, on January 6th, with one 

 by Murchison,* objecting to this absorption of the Lower 

 Silurian and reiterating his remark of 1843 that the fossil- 

 iferous . Cambrian beds were Lower Silurian in their fossils, 

 and arguing, thence, for the absorption of the Cambrian, to this 

 extent, by the Silurian. Having, eight years before, in his 

 great work on the " Silurian System," described the Lower 

 Silurian groups with so much detail, and with limits well 

 defined by sections and by long lists of fossils, over a hundred 

 species in all, many of them figured as well as described, and 

 having thus added a long systematized range of rocks to the 

 lower part of the Paleozoic series, be was naturally unwilling 

 to give up the name of Lower Silurian for that of Upper Cam- 

 brian or Cambro-Silurian. Moreover, the term " Silurian," 

 with the two subdivisions of the system, the Upper and Lower, 

 had gone the world over, having been accepted by geologists 

 of all lands as soon as proposed, become affixed to the rocks to 

 which they belonged, and put into use in memoirs, maps and 

 geological treatises. 



In 1852, the controversy, begun by encroachments not in- 

 tended on either part, reached its height. Sedgwick's earnest 

 presentation of the casef and appeal before the Geological 



* Q. J. Geol. Soc., iii, 165, Jan., 1847. f r ° id -. viii > 152 - 



