PHYSICAL AND FAUNAL EVOLUTION 201 
post-Saratogan, belonging to the basal portion of the Beekmantown 
series as generally defined. This is clearly true of the conglomeritic 
layer at the base of the Little Falls dolomite in the Mohawk Valley, 
and is probably also true of the so-called Potsdam of the Black River 
region and the westward continuation of the outcrop in Canada. 
There is good reason for beheving that the sea at the end of Saratogan 
time did not cover the present site of Lake Ontario, and that the 
basal sandstones of the Ontario region belong to the base of the over- 
lapping early Beekmantown. In some cases the basal sands (St. 
Mary’s sands) are even younger than this (Lowville, N. Y., Encamp- 
ment d’Ours, Isle Lacloche, etc.), for the immediately overlying 
strata carry late Chazy (Lowville) or even Black River fossils, and, so 
far as now known, there is no break in sedimentation between these 
basal sands and the beds immediately succeeding, which thus deter- 
mine their age. In all such cases, until positive evidence of a pro- 
nounced physical break or disconformity is determined between the 
two series, or until the basal bed is shown by unquestionable fossil 
evidence (exclusive of Scolithus, burrows, trails, and other problem- 
atic markings which may characterize various Paleozoic sand- 
stones) to be of Cambric age, logical reasoning compels us to regard | 
the age of the basal sandstone in each case as essentially that of the 
fossiliferous beds immediately succeeding, unless these are the very 
lowest post-Cambric beds. 
One other point should be clearly emphasized. It is by no means 
established that the basal sandstones are everywhere of marine 
origin. In fact, the general absence of fossils, the frequent cross- 
bedding and other characters point rather to a continental origin of 
a part, at least, of this basal series, the agents of deposition being 
rivers or the wind. ‘There is scarcely a geologist today who is satisfied 
with the complacent explanation, current only a short time ago, that 
the absence of fossils in a sandstone is due to “ unfavorable conditions 
at the time of deposition,” or to subsequent destruction of the fossils, 
in some mysterious way or other. That fossils abound in marine 
sandstones of all kinds, and even in conglomerates, is a well-known 
fact, and that the sands along our modern sea-shores are rich in 
shells and other hard parts of organisms, is equally a matter of 
common knowledge. The argument that the absence of fossils in a 
