534 



SCIENCE. 



[K S. Vol. XXII. No. 565. 



land, Maryland, but the typical salt and gyp- 

 sum-bearing Salina beds, such as furnish the 

 salt of Syracuse, have characters which seem 

 explicable only on the supposition that all 

 this region was a desert country, with much 

 evaporation and comparatively little rainfall, 

 and that the basins in which salt accumulated 

 were shallow pools, rarely, if ever, flooded by 

 the sea, the salt being bleached out of the sur- 

 rounding marine sediments by the occasional 

 rains and left by the evaporation of the water. 

 But here, as in the case of the Medina, much 

 detailed study of the lithic character of the 

 formation is necessary before we can do more 

 than make provisional hypotheses. We know, 

 however, that marine conditions were reestab- 

 lished ^over all New York towards the end of 

 Siluric time. As Hartnagel and Schuchert 

 have shown, the sea invaded eastern north 

 America by a transgression of the Atlantic 

 waters. Al the same time a trangression 

 from the southwest appears to have occurred, 

 which brought with it a different type of 

 fauna, the two together constituting the 

 Cobleskill. The Manlius limestones represent 

 typical marine conditions; but you will have 

 noticed that many of the lime mud-beds or 

 calcilutytes show mud cracks, which indicate 

 water so shallow that occasional emergence 

 was possible. The Manlius beds grade up- 

 wards into the fossiliferous calcarenytes, 

 which, as the Colymans limestones, form the 

 basal Devonic beds of the New York section. 

 This and the higher beds of the Helderbergian 

 series are now no longer found, except as 

 remnants, in this region, erosion having re- 

 moved most of them. You will bear in mind 

 that this erosion was a pre-Onondaga erosion, 

 for the Onondaga rests everywhere in this 

 region upon the eroded surfaces of the Coly- 

 mans or the Manlius. This erosion belongs 

 to Oriskany time, for continuous deposition 

 into the Lower Oriskany is shown by the 

 section at Becraft Mountain. What the 

 amount of erosion was and what the length 

 of time during which it was accomplished, 

 we have at present no means of judging. 

 There is every reason to believe that the high- 

 est Helderberg strata extended at least as far 

 as Syracuse, and there is reason to suppose 



that they extended farther and overlapped the 

 lower ones. But the Oriskany erosion has- 

 removed all this. The hiatus, though pro- 

 nounced, is scarcely noted by the casual ob- 

 server, because the formations are perfectly 

 conformable, so far as position of strata is 

 concerned. We need a term to express the- 

 relation where two formations thus conform 

 in their bedding, but comprise between them 

 a time break of greater or less magnitude. 

 To speak of such strata aS unconformable,, 

 without qualifying the term, is misleading, 

 since it suggests that the older strata have suf- 

 fered folding and erosion before the deposi- 

 tion of the later. Until a better term is pro- 

 posed, we might speak of such formations as' 

 cZisconformable, leaving the term unconform- 

 able for cases in which discordant relationship 

 of bedding occurs. 



The disconformable relation of the Onon- 

 daga upon the Manlius or Colymans is some- 

 times qualified by the occurrence of lenses of 

 Oriskany between them. The relationship of 

 the Oriskany and other overlying formations 

 is best brought out by the consideration of a 

 few sections. In the Hudson Valley the lowest 

 Oriskany — that of Becraft Mountain — is a 

 direct successor, without break of deposition, 

 of the uppermost Helderbergian, the Port 

 Ewen. It is succeeded by about three hun- 

 dred feet of dark argillaceous silicilutytes, the 

 lower part of which are the Esopus and the^ 

 upper the Schoharie. Above this come the 

 Onondaga limestones, the transition being a 

 complete, though rather rapid, one. In the- 

 Schoharie Valley later Oriskany rests on 

 eroded Helderbergs, and is followed by about 

 100 feet of the dark lutytes, mostly of Esopus- 

 or Caudagalli age. West of this region the 

 Oriskany occurs at irregular intervals, while- 

 the Esopus has thinned away. Finally, at 

 Cayuga Ontario, half-way between Buffalo 

 and Detroit, the uppermost Oriskany alone oc- 

 curs, resting on eroded lower Manlius and 

 intimately related with the overlying Onon- 

 daga. Here, then, is no room for Esopus or 

 Schoharie, for Onondaga is the direct and 

 immediate successor of latest Oriskany. This- 

 indicates a westward transgression of Oris- 

 kany sediments, the later beds overlapping- 



