October 27, 1905.] 



SCIENCE. 



533 



Ulster County a similar white quartz-pebble 

 conglomerate, the Schawangunk grit, lies un- 

 conformably upon the upturned and eroded 

 Hudson Eiver beds, and is followed by less 

 than a hundred feet of red lutytes and 

 arenytes, and then by the cement beds, which, 

 by their enclosed fossiliferous bands, prove 

 their identity with similar beds overlying the 

 Salina in western New York. Close inspec- 

 tion of the series shows continuity of deposi- 

 tion, which proves the age of the red beds and 

 the Schawangunk conglomerate to correspond 

 to that of the New York Salina. Still further 

 east, in Rensselaer County, a similar con- 

 glomerate, the Rensselaer grit, rests uncon- 

 formably on Cambric and Hudson beds. How 

 shall we interpret these sections ? At the end 

 of Ordovicic time the folding of the Ordovicic 

 strata of eastern United States took place — • 

 what is familiarly known as the Green Moun- 

 tain revolution. So far no strata later in age 

 than Lorraine have been found in these folded 

 beds; hence it is safe to assume that strata 

 of Richmond age were never deposited in 

 eastern United States; in other words, that 

 the folding began at the end of Lorraine time. 

 This folding was, no doubt, accompanied by 

 an elevation of the land, and a westward re- 

 treat of the interior sea. Elevation of an old 

 land is commonly followed by vigorous stream 

 activities, which results in erosion. In the 

 present case the products of this erosion were 

 spread by the streams over the land exposed 

 by the retreating sea. This is the ultimate 

 mode of origin of the conglomerates in question 

 and of the red sandstones. The red colors of 

 the sands and muds indicate that they are the 

 product of the subaerial decay of rocks; and 

 the only rocks at all competent to furnish the 

 material of these strata are the crystallines 

 of the Appalachian old land, as long ago 

 pointed out by Davis and others. That the 

 conglomerates and their representative in 

 western New York, the basal sandstone of 

 the Medina, are, in part at least, river de- 

 posits, later on worked over by the sea, seems 

 unquestionable, for though the retreating sea 

 would wash out seawards the materials of the 

 shore, such thick masses of pebbles can hardly 



be carried so far from their source without 

 the aid of rivers. A comparison of the Siluric 

 sections of the Appalachians suggests that the 

 conglomerates and sandstones are part of a 

 huge subaerial fan, whose apex was in south- 

 eastern Pennsylvania, and which thinned 

 away radially in all directions. That a part 

 of this fan was formed during Richmond 

 time seems probable, and is further indicated 

 by the occurrence of marine Ordovicic fossils 

 in what was probably the margin of the fan 

 in Virginia. However, a great deal of care- 

 ful comparative study is needed to unravel 

 the complete history of these deposits.^ 



In central United States the Richmond is 

 succeeded by marine deposits commonly cor- 

 related with the Clinton of New York. 

 Though land conditions, accompanied by 

 erosion, are indicated in many localities, in 

 some cases the lowest Siluric sediments seem 

 to rest directly upon the highest Ordovicic. 

 It is impossible to determine from the litera- 

 ture whether in any of these cases continuous 

 deposition occurred or not. Further field ex- 

 aminations will have to settle that. Marine 

 conditions came into existence again in west- 

 ern New York in Upper Medina time, and 

 gradually transgressed eastward. The Siluric 

 sea reached as far as Utica in Upper Medina 

 time, but did not reach Ulster County until 

 the conditions of the deposition of the Salina 

 beds were instituted in central and western 

 New York — if at that time marine conditions 

 existed at all in New York. The continued 

 red sedimentation, which is so pronounced 

 throughout the Sali-na sediments and which 

 appears to indicate a continuous supply of 

 highly oxidized material from the old land 

 on the east, and, further, the presence of true 

 Salina strata only along the inner margin of 

 the Appalachians, their great thickness in the 

 east and their thinning away to the west, all 

 suggest that land conditions, rather than 

 marine, existed in this period. That marine 

 deposits were forming in some region is indi- 

 cated by such sections as that near Cumber- 



^ Investigations of this problem are now in 

 progress under the auspices of the New York 

 State Geological Survey. 



