214 AMADEUS W. GRABAU 
To make a distinct system of them, as has been proposed by some, 
will not solve the difficulty, because the transitional beds are likely 
to be of very variable quantitative and chronologic values in different 
localities. The accepted base of the Ordovicic,—the summit of the 
Saratoga formation in New York, of the Franconia sandstone in the 
Mississippi Valley, and of the Asaphellus homjrayi beds on the 
Atlantic coast, is a perfectly satisfactory one, as long as the syn- 
chroneity of these formations is granted. (Compare Figs. 1 and 2.) 
REGRESSIONAL PHASE OF THE BEEKMANTOWN 
As has been fully demonstrated by the author elsewhere’ and 
by Berkey,’ the chief event of Beekmantown time in North America 
was the widespread regressive movement of the sea and the re- 
emergence of the continent. The extent of the movement is shown 
by the extensive disconformity between the Beekmantown and the 
succeeding Chazy formations. From this it appears that only a 
narrow trough remained in the Appalachian region as the sole repre- 
sentative of the interior or Mississippian sea, while most of the 
Pacific coast region, west of the Rocky Mountains axis, was prob- 
ably uncovered (see map, Fig. 3). In the interior of North America 
the emergence was accompanied by widespread continental deposi- 
tion recorded in the St. Peter sandstone. The detailed character- 
istics of this formation; the all but complete absence of fossils; the 
cross-bedding shown in many exposures; the rounded character of 
the sand grains, their grooved and pitted surfaces; the absence of 
the finer impurities; the uniformity of the size of grain in the same 
region—all point to long-continued shifting about of these sands. 
by winds, and testify against their marine origin. The inclusions. 
in the quartz grains show them to be derived from the crystalline 
oldland, the chief source being probably the Canadian shield. In 
some cases the contact with the underlying formations is abrupt and 
disconformable, showing that erosion of the uncovered limestones. 
preceded the deposition of the sands. Not infrequently the contact 
t Grabau, A. W., ‘‘ Physical Characters and History of Some New York Forma- 
tions,” Science, N. S., Vol. XXII., pp. 528 ff., October, 1905; also, ‘“‘Types of Sedi- 
mentary Overlap,” Bull. Geol. Soc. Amer., Vol. XVII, pp. 616 ff. 
2 Berkey, C. P., ‘‘Paleogeography of St. Peter Time,” Bull. Geol. Soc. Amer., 
Vol. XVII, pp. 229-50. 
