410 CAMBRIAN AND SILURIAN IN NORTH AMERICA. [XV. 



their maximum size at this period, and that forms were present 

 representative of almost every stage in development, from the 

 little Aynostus with two rings to the thorax, and Microdiscus 

 with four, to Erinnys with twenty-four, and blind genera along 

 with those having the largest eyes, leads to the conclusion that 

 for these several stages to have taken place numerous previ- 

 ous faunas must have had an existence, and, moreover, that 

 even at this time in the history of our globe an enormous pe- 

 riod had elapsed since life first dawned upon it." 



The facts insisted upon by Hicks do not appear to be in- 

 consistent with the view that at this horizon the trilobites had 

 already culminated. Such does not, however, appear to be 

 the idea of Barrande, who in a recent learned essay upon the 

 trilobitic fauna (1871) has drawn from its state of development 

 at this early period conclusions strongly opposed to the theory 

 of derivation. 



The strata holding the first fauna in southeastern Newfound- 

 land rest unconformably, according to Mr. Murray, upon what 

 he has called the Intermediate series ; which is of great thick- 

 ness, consists chiefly of crystalline rocks, and is supposed by 

 him to represent the Huronian. He has, however, included in 

 this intermediate series several thousand feet of sandstones 

 and argillites which, near St. John's in Newfoundland, are seen 

 to be unconformably overlaid by the fossiliferous strata already 

 noticed, and have yielded two species of organic forms, lately 

 described by Mr. Billings. One of these is an Arenicolites, 

 like the A. spiralis found in the Lower Cambrian beds of Swe- 

 den, and the other a .patella-like shell, to which he has given 

 the name of Aspidella Terranovica. (Amer. Jour. Science 1 (3), 

 III. 223.) These, from their stratigraphical position, li.-ivo 

 been regarded as Huronian ; but from the lithological descrip- 

 tion of Mr. Murray, the strata containing them appear to be 

 unlike the great mass of the Huronian rocks of the region. 

 Their occurrence in these strata, in either case, marks a down- 

 ward extension of these forms of palaeozoic life. 



Mr. Billings has described from the rocks of the first fauna 

 certain forms under the name of Archeocyathus, one of the 



