192 PALEOZOIC TIME. 



H. ; I. Bayfeldi B. ? ; Asaphus obtusus H. ; Buthyurus Angelini B. ; Amphion Canaden- 

 sis B. 



b. Ostracoids. — Fig. 316, Leperditia Canadensis Jones, from Grenville, Huntley and 

 elsewhere in Canada; L. amygdalina B., from near L' Original, Canada. 



The Mollusks common to the Calciferous and Levis, according to Billings, are Lingula 

 ManteUi, Camerella Calcifera and Pleurotomaria Calcifera (and possibly also Ophileta 

 uniangulata, Maclurea matutina, M. sordida, Holopea dilucula). Only the Camerella 

 varians is common to the Chazy and Levis. In the lower part of the beds underlying 

 the true Levis beds of Cow Head, Newfoundland, which have been called Upper Cal- 

 ciferous by Logan, there are seven trilobites, of which Amphion Barrandei and Asaphus 

 canalis occur in the Levis. Ortliis Electra is also common to these beds and the Levis; 

 but the other fossils are either new species, or species that occur in the Chazy and Cal- 

 ciferous. Above these beds, there are 277 feet of rock with still another fauna: and 

 then follow 700 feet of sandstone, and then the true Levis formation, at Cow Head. 



European. 



Although in North America the rocks of this period have an aggre- 

 gate thickness of more than 7,000 feet, with 3,000 feet of them lime- 

 stones, and some of them abound in fossils, their precise equivalents 

 in Europe are not well understood. This is part of the proof that 

 geological changes over the different continents have to a large extent 

 gone forward independently. All that can be positively said is, that 

 the American strata correspond to the lower part of the Lower Silu- 

 rian, above the Primordial, in Europe — and probably to (1) the Tre- 

 madoc slates, and (2) the Arenig or Stiper Stones group (Lower Llan- 

 deilo) in England; the lower part of Barrande's stage D, in Bohemia,, 

 and Angelin's group BC in Sweden. 



Among the fossils of the Tremadoc slates, there occur Trilobites of the genera Dicel- 

 loatphalus, Conocoryphe, Olenus, Cheirurus, Angelina, Asaphus; also the Lingulella Da- 

 visii M'Coy, a Lingula-flags species. The Stiper Stones, quartzose strata in Shropshire, 

 contain the burrows of Annelids (like Arenicolites linearis H.), which, however, are an 

 uncertain mark of age. But beds in Arenig Mountain in Merionethshire, and the Skid- 

 daw slates in the lake district of Cumberland, which are of the same age, have afforded 

 over sixty species of fossils — among them, Obolella plumbea S., Didymograptus gemi- 

 nus Hisinger, D. hirundo Hisinger, Ogygia Selwynii S., vEglina binodosa S- and other 

 species that are not Primordial, and are distinct from the species of the overlying Llan- 

 deilo flags (Lyell). H. A. Nicholson has announced that fourteen species of Grapto- 

 lites, from the thirty-one in the Skiddaw slates, are species which Hall has described 

 from the Quebec group of Canada (Q. J. G. Soc, xxviii. 217). 



3. General Observations. 



While the rocks of the Primordial era, over the larger part of North 

 America, are chiefly sandstones, and but sparingly limestones, and 

 bear evidence, in most places, of shallow waters and of currents bear- 

 ing sediments, — those of this second period of the Lower Silurian 

 are as prominently limestones, and over large regions are indications 

 of clear seas. But, while limestones are the prevailing rock, all 

 regions over the continent were not contemporaneously making lime- 



