560 A. W. GRABAU LOWER ORDOVICIC FORMATIONS 



of sedimentation, so far as known, but is accompanied by the most pro- 

 nounced faunal change, since it marks the appearance of f aunal elements 

 generally regarded as typical of the Siluric. The corresponding Ameri- 

 can systems would be the Beekmantownian (including the Ozarkian, in 

 a modified sense, as the transgressive phase 5 ), the Chazy-Trenton, and 

 the Eichmondian. As will be shown later, however, the pre-Eichmond 

 emergence was not comparable in magnitude to the emergence marking 

 the end of Beekmantown time. Schuchert uses the terms Canadian, 

 Champlainian, and Cincinnatian for these three diastrophic cycles; but 

 in his Cincinnatian he includes what is most certainly a part of the 

 emergence phase of his Champlainian cycle, namely, the Utica shale. 

 The Chazy and Trenton were included by Dana in the first edition of his 

 manual in the Trenton period, which is essentially equivalent to Schu- 

 chert' s modified Champlainian (not the Champlainian of Clarke and 

 Schuchert, 1899). The Utica and higher beds were placed by Dana in 

 the Hudson period in 1863, but included with the Trenton limestone 

 (inclusive of the Black Eiver and "Birdseye") in the Trenton period in 

 the fourth edition in 1895, when he placed the Chazy within the Cana- 

 dian. It is in this sense that I here use the term Trentonian, a term 

 essentially equivalent to the English Caradocian. 



Lower Ordovicic oe North Scotland and its Eelation to similar 



Deposits Elsewhere 



general petrographic and faunal characteristics 



One of the remarkable features of the early Paleozoic rocks of Britain 

 is the striking difference in character and faunas between the Cambric 

 and Ordovicic rocks of the northern and of the southern area. The 

 southern area, which comprises all the regions south of the Scottish High- 

 lands, includes the type regions for the Cambric, Ordovicic, and Siluric 

 formations, which are for the most part developed in their terrigenous 

 facies as quartzites, graywackes, sandstones, and mudstones, while lime- 

 stones are more rarely represented. The prevailing element of the en- 

 tombed faunas is furnished by the graptolites, though trilobites are also 

 of frequent occurrence. It is this southern or English fauna which has 

 its close analogue in northeastern North America (New Brunswick, Cape 

 Breton, eastern Newfoundland, eastern New England, etcetera), and 

 the faunas found in these beds must be regarded as representing that of 

 the somewhat expanded Atlantic of that time. 



5 This is the Potsdam period of the first edition of Dana's "Manual" (1863), which he 

 divided into, 1, Potsdam epoch, and 2, Calciferows epoch. 



