APPLICATION OP PRINCIPLE OF TRANSGRESSIVE OVERLAP 585 



Scolithes canadensis. The section terminates with a concretionary bed, 

 which at Grenville, where these fossiliferous beds rest directly upon the 

 crystallines, is followed conformably by Chazy. Unless there is an un- 

 recognized hiatus here, the Calciferous of this section represents only the 

 uppermost Beekmantown of the Champlain valley, where this formation 

 has a thickness of 1,800 feet, according to Brainard and Seeley.* If this 

 is the case, then the Potsdam of this series, since it forms a continuous 

 series with the Beekmantown beds overlying, is also of Beekmantown age ; 

 for it is hardly conceivable that under apparently uniform conditions 

 1,800 feet of limestones should accumulate in the Champlain valley, while 

 less than 100 feet accumulated in the Ottawa region. Even if a hiatus 

 exists between the Beekmantown and Chazy of the Ottawa Eiver sections, 

 we can still regard the Calciferous and Potsdam of these sections as above 

 the base of the Beekmantown of the Champlain valley, since the fauna is 

 more comparable to that of the later Beekmantown of the Champlain 

 valley. If this deduction is sound, it leads us to question the Cambric 

 age of all the Potsdam of the Ottawa river and the Riviere du ISTord. The 

 fossils found in this basal sandstone are the worm tube Scolithes cana- 

 densis, and the peculiar tracks called Protichnites, besides Lingulepis 

 acuminatus, Ophileta compacta, Pleurotomaria cf. lawrentina, and frag- 

 ments of Orthoceras. The species of gastropods are also characteristic of 

 the Calciferous of these regions, in which formation also occurs a species 

 of Scolithes. Lingulepis acuminata is not strictly a Cambric fossil, for 

 the species is found to range up into the Beekmantown at Whitehall, 

 New York, and in Saint Lawrence county. Ophileta compacta also 

 occurs in the upper beds of the Chateaugay section in what is considered 

 typical Potsdam sandstone, associated with Lingulepis acuminata, Dicel- 

 locephalus sp. ?, and Ptychaspis sp. ?f 



One hundred and fifty miles up the Ottawa from Grenville, at the 

 Allumette rapids, near Pembroke, the Chazy rests with a basal conglomer- 

 ate upon the gneiss, and at Saint Ambroise the Trenton rests upon the 

 crystallines with only 20 feet of sandstones intervening. This sandstone 

 has been referred to the Potsdam, but it is more probably referable to the 

 lower Trenton. 



Basal Paleozoic beds of the Pocky Mountain region. — Wherever the 

 Paleozoics are exposed in contact with the crystallines, a basal sandstone 

 or conglomerate forms the base of the series. In a number of localities 

 this basal sandstone (Sawatch quartzite) carries a Dicellocephalus fauna, 

 as in Gunnison county (Crested Butte), at Aspen, the Eagle river and 



* Bull. Amer. Mus. Nat. Hist., vol. iii, 1890, no. 1, pp. 2, 3. 

 i Walcott : Correlation papers, Cambrian, p. 343,347. 



