364 GEOLOGY. 



orders; and it is not improbable that the mental development also 

 approached somewhat nearly to that now possessed by correspondingly 

 low types. Higher biological types within the same orders have cer- 

 tainly been developed since in many cases, and probably higher mental 

 functions; but some of the Ordovician forms have since suffered bio- 

 logical degeneration, and probably also mental degeneration. The 

 Ordovician ancestor of the barnacle, a free-moving active form, was 

 doubtless superior to his sessile descendant of ill-repute. The sum 

 total of ecological adaptation, and of social and mental development, 

 however, seems to have advanced with each era, though perhaps not 

 always with each of the briefer stages. 



The Succession of Faunas. 



i. The Fauna of the Calciferous. — The Calciferous in its typical develop- 

 ment, in New York and the interior, is usually very poor in fossils, and these are 

 poorly preserved. It is therefore difficult to find species that have a wide geo- 

 graphical range and yet are known to be so closely confined to this horizon as 

 to be characteristic of it. Of the species so regarded the most widely avail- 

 able is the gastropod, Ophileta complanata (Fig. 161, A; and I). 



Certain genera are usually present, however, in most faunas of this age, among 

 which may be mentioned Tryblidium and Eccyliomphalus among tlie gastropods, 

 Syntrophia and Camarella among the brachiopods, Orthoceras and other genera 

 among the cephalopods, and Bathyurus among the trilobites. 



Doubtless many more or less imperfectly known species are really charactQr- 

 istic of the formation, but are not sufficiently prevalent and well preserved to 

 give good evidence of it. Of connecting species, and hence not characteristic 

 ones, there is a small list of which some range below and some above. For the 

 greater part, the fossils are so sparse and so imperfect that their range and sig- 

 nificance is not determinable. In the Champlain and the lower St. Lawrence 

 Valleys where the formation is greatly thickened and appears to be less sharply 

 distinguished from the formations below and above, a more ample fauna is found, 

 and in it more species that range into the overlying and underlying formations. 

 Thirty-five genera and one hundred species are announced from the vicinity of 

 Lake Champlain, but the ranges of these have not yet been determined, 1 



In the shales of the Levis formation in the lower St. Lawrence Valley many 

 graptolites are found. These belong to the Phyllograptus zone, which embraces 

 the subzones of Tetragraptus and of Didymograptus bifidus. 2 They represent 

 a horizon corresponding to the Arenig of Great Britain. The Tetragraptus is 



1 Brainard and Seeley, Bull. Geol. Soc. Am., Vol. I, 1890, pp. 501, 513; Vol. II, 

 1891, pp. 293, 300; Whitfield, ib., Vol. I, pp. 514,515. 



2 Lapworth, Trans. Roy. Soc. Can., 1886; also Ann. Rep. Geol. Surv. Can., 1877-88, 

 Part II, p. 45K; also Ann. Nat. Hist., 5th Series, Vol. VI, 1880, p. 197. 



