110 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The Sharon (Olean) Conglomerate, mentioned in the state reports 
as “a round pebble conglomerate” (Lesley et al., p. 1721), is described 
by I. C. White as being everywhere a very massive, coarse, grayish- 
white, pebble rock, the pebbles varying in size from a pea to a hen’s 
egg, all cemented into a matrix of coarse gray sand, and frequently 
containing vast quantities of imbedded plant remains (I. C. White, 
p- 37). 
The thickness of the Pottsville Conglomerates in the anthracite 
district averages 1200 feet in Carbon, Schuylkill, Lebanon, and 
Dauphin counties but it diminishes rapidly toward the north-north- 
west in Luzerne and Lackawanna counties. The reduction in thick- 
ness is accompanied by a decrease in the coarseness of materials; the 
pebbles become scattered and are no larger than a pea (Lesley et al., 
p. 1854). Stevenson, who has studied the Pottsville formation from 
the stratigraphic standpoint, concludes that the thinning out toward 
the northwest is due to the successive disappearance of the lower 
members, so that in much of the northern field even the Sharon sand- 
stone has but an insignificant representation (Stevenson, p. 202). 
Thus his results agree with the palaeobotanical studies of David White 
in placing the apparently basal conglomerates in the thin northwestern 
sections high up in the columns of the thicker, more easterly sections. 
Bailey Willis, after noting some of the characteristics already men- 
tioned, brings out the additional feature of lenticular form, which 
appears to be common in the Pottsville and later Carboniferous 
deposits, so that a bed of sandstone, shale, or coal thins out and is 
replaced in its own horizon by deposits of different texture (Willis, 
© Pio) 
It will be noted that the Pottsville formation presents a numberof 
contrasts to the Cretaceous system of Texas. The variability of com- 
position, assortment, and color in the lower members and the rapid 
diminution in thickness and size of materials toward the north-north- 
west are especially noteworthy when compared with the relative 
uniformity of the Texas series over wide areas. Recent unpublished 
studies by members of the New York State survey throw doubt upon 
the marine origin of the Pottsville rocks. Professor Grabau, in & 
recent (1906) unpublished address to’ the Geological conference of 
Harvard University, expressed the view that the Pottsville series 
represent, on the whole, a great alluvial fan, which in its growth ex- 
tended progressively northwestward. The Pottsville Conglomerate 
cannot, therefore, be regarded as a typical marine deposit. More 
probably it should be classed among fluviatile deposits, which in recent 
