DEVONIAN AGE. 280 



which does not appear above the Upper Silurian in America, but is 

 found in the Eifel limestone in Europe; that of Trilo bites, which, 

 after there had been, under a succession of genera, over 1,700 species, 

 came nearly to its end with the Devonian, the old genera being all ex- 

 tinct, and only three new ones appearing in the Carboniferous, to close 

 off this prominent Paleozoic type ; the Ortkoceras family, species of 

 which were few after the Devonian age. Extinction here means 

 merely no reappearance among known fossil remains. The types may 

 have long afterward had representatives in the deep ocean if not in 

 some shallow seas. Loven reports the existence of a Cystid among 

 the living species of the deep Atlantic. 



(c.) In the historical changes in tribes or genera : for example, the 

 Spirifers, which began in narrow species in the Upper Silurian, be- 

 came broad-winged and very numerous in the Devonian, and continued 

 thus into the Carboniferous ; the species of Productus, the earliest of 

 which were very small and few, were afterward of large size and nu- 

 merous. 



Each of these points admits of extensive illustration ; but the above 

 is sufficient to give an idea of the kind of progress life was under- 

 going. Each period had its new species or tribes, and its extinctions, 

 and often, also, there were many successive faunas in a single period. 

 Families and tribes were in constant change; and, through all these 

 changes, the system of life was in, course of development. 



Climate. — The occurrence in the Arctic region of Devonian species, 

 of the Hamilton era of the United States (p. 266), shows that there 

 was little diversity of temperature at that time between the temperate 

 and Arctic zones. 



4. DISTURBANCES CLOSING THE DEVONIAN AGE. 



In eastern Canada, Nova Scotia, and Maine, the Devonian and Si- 

 lurian strata are uplifted at various angles beneath unconformable beds 

 of the Carboniferous ; and many of them have undergone more or less 

 complete metamorphism (Dawson, Logan, C. Hitchcock),. Dawson 

 says that " in the Acadian Provinces, in passing downward from the 

 Carboniferous to the Devonian, we constantly find unconformability," 

 and part of the granyte of Nova Scotia " belongs to the close of the 

 Devonian." Again, in New Brunswick and Maine, the Devonian beds 

 near Perry underlie unconformably the Carboniferous ; the latter rest- 

 ing, with small dip, on the upturned edges of the plant-bearing De- 

 vonian strata. It appears then that an epoch of great disturbance 

 over the Eastern-border region intervened between the Devonian and 

 Carboniferous ages. 



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