XV.] CAMBRIAN AND SILURIAN IN EUROPE. 357 



tions, 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 Cam- 

 brian rocks different from those of the Lower Silurian series. 

 If the appeal to nature should be answered in the negative, 

 then it was clear that the Lower Silurian type must be consid- 

 ered 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 palaeozoic 

 base would necessarily be removed 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 zoolog- 

 ical classification, it being, in that sense, synonymous with 

 Lower Silurian." That such was the result of pala3ontological 

 inquiry, Murchison proceeded to show by repeating the an- 

 nouncements already made by Sedgwick in 1837 and 1838, 

 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 further declared by Murchison in this address, 

 that researches in Germany, Belgium, and Eussia led to the 

 conclusion that the " fossiliferous strata characterized by Lower 

 Silurian Orthidae are the oldest beds in which organic life has 

 been detected." (Proc. Geol. Soc., III. 641, et seq.) The 

 Orthids here referred to are, according to Salter, Orthis calli- 

 gramma, Dalm, and its varieties. (Mem. Geol. Survey, III. 

 Part II. 335 - 337.) 



Meanwhile Sedgwick's views and position began to be mis- 

 represented. In 1842, Mr. Sharpe, after calling attention to 

 the fact that the fossils of the Bala limestone were, as Sedgwick 



