CONCLUSIONS AS TO SHAWANGUNK AND LONG WOOD DEPOSITS 527 



in the region now forming southern New York and northern New Jersey, 

 and spread out northward, westward, and southward to the borders of 

 the contracted Niagaran Sea, in which the last survivors of the marine 

 Guelph types existed. Besides some of the river-borne sediment, in- 

 numerable carapaces and perhaps many living Eurypterids were. carried 

 into this sea, which at times may have been converted into a fresh-water 

 body. With continued aridification of the climate, owing probably to a 

 progressive rise of the old-land region and a further obstruction of the 

 moisture-bearing winds from the east, the interior water body was com- 

 pletely evaporated and its salt content laid down in the deeper depres- 

 sions. Continued aridity permitted the deposition of the oxidized muds 

 and oxidized sands now forming the red sandstones and shales, while 

 salt and gypsum derived from the leaching and disintegration of the old 

 marine sediments were accumulating in the central basin. This period 

 was brought to a close by the transgression of the Upper Silurie or Lower 

 Monroan Sea from the general region of Maryland southward and west- 

 ward. A part of the Salinan red sediments was reworked and incor- 

 porated as marine sediments with ostracods, etcetera, in the Lower 

 Monroan, which elsewhere is a pure clastic lime-mud rock. The Camillus 

 shale of New York may, in part at least, belong to this period. Finally, 

 in Upper Monroan time, open connection with a southern sea in the 

 Pennsylvania and Maryland region permitted the extensive growth of 

 the Stromatopora and coral reefs with their attendant clastic deposits. 

 These extended into Michigan and probably joined a similar transgres- 

 sion of the Pacific from the northwest. The peculiar basins in which 

 the Bertie water-lime was forming belong to this period, and they were 

 eventually superseded by the extended transgression of the sea, which 

 made the widespread development of the Cobleskill formation possible. 

 The Manlius-Lucas epoch succeeding marks the widespread reestablish- 

 ment of marine conditions in North America.* 



It should be noted that the clastic deposits of the Upper Silurie period 

 still denote a general arrangement of easterly winds, and of high lands 

 on the eastern border of the continent to intercept them, and the eon- 

 sequent prevalence of arid or semiarid conditions on the western slopes 

 of this land. A fact which may have considerable significance is that 

 the centers of deposition had shifted to the northeast, having been in 

 Tennessee and in central Pennsylvania in Upper Ordovicic time, but in 



♦These marine transgressions and the changes during the succeeding periods are fully 

 discussed in the monograph on the Devonic Formations <>J' Michigan, now nearing com- 

 pletion. 



