No. 3.] iFIUNT — ON CAMBRIAN AND SILURIAN. 287 



ment. not less so to the discoverer of the Upper Cambrian series. 

 Meanwhile, the latter, as we have seen, in 1842 re-exauiined 

 with Salter his Upper Cambrian sections in North Wales, and 

 satisfied himself of the correctness, both structurally and paleon- 

 toloi»;ically, of his former determinations. Murchison, in his an- 

 niversary address as President of the Geological Society in 1842, 

 after recounting, as we have already done, the history of the 

 naming by Sedgwick in 1835, of the Cambrian series, which 

 Murchison supposed to underlie his Silurian system, proceeded 

 as follows : " Nothing precise was then known of the organic con- 

 tents of this lower or Cambrian system except that some of the 

 fossils contained in its upper members in certain prominent lo- 

 calities were published Lower Silurian species. Meanwhile, by 

 adopting the word Cambrian, my friend and myself were certain 

 that whatever might prove to be its zoulogicd distinctions, this 

 great system of slaty rocks being evidently inferior to those zones 

 which had been worked out as Silurian types, no ambiguity could 

 hereafter arise. * * * In regard, however, to a descending 

 zoological order it still remained to be proved whether there was 

 any type of fossils in the mass of the Cambrian rocks difi"erent 

 from those of the Lower Silurian series. If the appeal to na- 

 ture should be answered in the negative, then it was clear that 

 the Lower Silurian type must be considered the true base of 

 what I had named the protozoic rocks ; but if characteristic new 

 forms were discovered, then would the Cambrian rocks, whose 

 place was so well established in the descending series, have also 

 their own fauna, and the p ileozoic base would necessarily be re- 

 moved to a lower horizon." If the first of these alternatives 

 should be established, or in other words, if the fauna of the 

 Cambrian rocks was found to be identical with that of the Lower 

 Silurian, then, in the author's language, " the term Cambrian 

 must cease to be used in zoological classification, it being, in that 

 sense, synonymous with Lower Silurian." That such was the 

 result of paleontological inquiry, Murchison proceeded to show 

 by repeating the announcements already made by Sedgwick in 

 1837 and 183i^, that the collections made by the latter from the 

 great series of fossiliferous strata in the Berwyns, from Bala, 

 from Snowdon and other Cambrian tracts, were identical with the 

 Lower Silurian forms. These strata, it was said, contain 

 throughout " the same forms of Orthis which typify the Lower 

 Silurian rocks." It was farther declared by Murchison in this 



