XV.] CAMBRIAN AND SILURIAN IN NORTH AMERICA. 425 



selves (the Cambrian of Murchison and the geological survey), 

 for the reason that the primordial fauna has now been shown 

 by Hicks to extend towards their base. This, although con- 

 sistent with Earrande's previous views as to the extension of 

 the name Silurian, is a still greater violation of historic truth. 

 By thus making the Silurian system of Murchison to include 

 successively the Upper Cambrian and the Middle Cambrian 

 of Sedgwick, and finally his Lower Cambrian (the Cambrian 

 system of Murchison himself), we seem to have arrived at a 

 reductio ad absurdum of the Silurian nomenclature ; and we 

 may apply to Siluria, as Sedgwick has already done, the apt 

 quotation once used by Conybeare with reference to the Gray- 

 wacke of the older geologists, which it replaces : " Est Jupiter 

 quodcunque vides" 



It would be unjust to conclude this historical sketch of the 

 names Cambrian and Silurian in geology, without a passing 

 tribute to the venerable Sedgwick, who to-day, at the age of 

 eighty-seven years, still retains unimpaired his great powers of 

 mind, and his interest in the progress of geological science.* 

 The labors of his successors in the study of British geology, 

 up to the present time, have only served to confirm the exacti- 

 tude of his early stratigraphical determinations ; and the last 

 results of investigations on both continents unite in showing 

 that in the Cambrian series, as defined by him more than a 

 generation since, he laid, on a sure foundation, the bases of 

 palaeozoic geology. 



* See the Preface to this paper for a notice of his death. 



