46 AMADEUS W. GRABAU 



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 believing 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 



