216 AMADEUS W. GRABAU 
is as sharply marked as that of aeolian quartz sands found upon the 
clear-swept limestone floors of some modern deserts.' In some cases, 
however, there appears to be absolute conformity between the St. 
Peter sandstone and the underlying dolomites, pointing to con- 
tinuous deposition. Both in Wisconsin and in Minnesota, the lower 
Magnesian beds are often slightly folded, and the lower St. Peter 
sandstone is likewise involved in these folds? (Fig. 4). The upper 
St. Peter, however, and the overlying Stones River, which are per- 
fectly conformable, are not involved in these folds. In Minne- 
sota, the Oneota, New Richmond, and Shakopee formations have 
a combined thickness of 105 to 260 feet. Jf the Jordan and St. 
Lawrence beds are regarded 
as Ordovicic, though they still 
contain Dicellocephalus, the 
thickness is increased to 190 
feet minimum) “or +072 “eet 
maximum. ‘The faunas of all 
the beds of the Lower Mag- 
nesian series indicate lowest 
Ordovicic and close relation- 
Fig. 4.—Showing the relationship of the 
Upper Stones River (S. R.) and lower Beek- 5 : 
mantown (B.) Beds of Minnesota and the ship to the Upper Cambric. 
included St. Peter (St. P.) (Redrawn from Jn the Black River region, 
Paleepdesardccony) Cushing records 20 to 60 
feet of lowest Beekmantown (Theresa), succeeded disconform- 
ably by Upper Chazy (Pamelia and Lowville limestones). The 
base is probably not exposed in this section, the basal sandstone, 
called Potsdam by Cushing, being most likely of later age. In the 
Mohawk Valley, 350 feet of Beekmantown (Little Falls dolomite) 
is followed disconformably by Upper Chazy (Lowville); but here, 
too, the base of the Beekmantown is not shown, and hence the true 
thickness is unknown. In the Lake Champlain region the Beekman- 
town is 1,800 feet thick; in southern Pennsylvania 2,250 to 2,300 feet; 
in central Pennsylvania nearly 2,500 feet; and in the Arbuckle Moun- 
tains of Oklahoma 1,250 feet. In all these localities, except central 
Pennsylvania, the upper limit of the Beekmantown is marked by a dis- 
«Compare Zittel, Beztrage zur Geologie und Palaeontologie der lybischen Wiiste. 
2 Hall and Sardeson, Bull. Geol. Soc. Amer., Vol. III., pp. 354, 355- 
