486 Prof. Sedgwick on the May Hill Sandstone, 



Stenopora fibrosa, Palaopora interstincta. 



Halysites catenulatus. Pentamerus linguiferus ( -|- un- 



Petraia (an unnamed species, datus), 



same as at May Hill). globosus. 



bina. oblongtLS. 



uniserialis, Hemithyris hemispharica, 



• subduplicata. Leptana transversalis. 



rugosa (?). Spirigerina reticularis. 



Of characteristic Cambrian species (i, e. of species which have 

 not been found among any admitted Upper Silurian rocks), not 

 one occurs in the above list. But all the above species are found 

 in the Wenlock or May Hill beds. And I may remark that here 

 (as at Norbury), nearly on the line of demarcation between Cam- 

 bria and Siluria, the common species seem to be crowded together, 

 and we might say that the old characteristic types had disap- 

 peared, and that the new and characteristic Silurian types had 

 not yet found time and place to develope themselves on the 

 section. 



On the joint evidence of this and the preceding section, we 

 may therefore conclude that we have found a true May Hill 

 group — a palseontological and physical base to the Silurian rocks, 

 — that this base does not lose its character by a blending within 

 it of the characteristic Cambrian and Silurian types, and hence 

 that (spite of the enormous dislocations of the country) it does 

 give us, though in a disjointed and fragmentary form, the ele- 

 ments for the construction of a good geological horizon. I do 

 not, however, believe that this horizon would have been dis- 

 covered in the country above described, had not its place been 

 made out before, by the incomparably clearer sections in North 

 Wales and the bordering English counties. 



I here conclude the details connected with the establishment 

 of the May Hill sandstone as a group not to be confounded with, 

 or united to, the Cambrian rocks. It was deposited after, or 

 during, great mechanical movements, and it seems exactly to 

 mark the epoch when the characteristic types of an older fauna 

 disappeared, and when the characteristic types of a newer fauna 

 began. If the facts above stated be not invalidated by opposing 

 evidence (and of this I have little fear, as I have now examined 

 the very places where it had been thought that there was some 

 opposing evidence), the discussion of them is no idle battle of 

 mere words, but involves fundamental principles essential to a 

 right classification, and consequently a right nomenclature of our 

 older Palaeozoic series. No classification, therefore, or nomen- 

 clature which has overlooked the place and office of the May Hill 

 sandstone can rest on a basis that is secure, or have any claim 

 for a permanent acceptance. 



