MID-SILURIC DELTA FANS OF NORTH AMERICA 47d 



nent, with the possible exception of the northeastern area in Nova Scotia 

 and adjoining districts, the top of the Xiagaran, where not followed by 

 the Salina deposits, shows evidence of erosion prior to the deposition of 

 the Upper Siluric or later formations over it. The Salina deposits ex- 

 tend from the Helderberg and Kittatinny Mountains on the east to 

 Michigan on the west. The southern boundary extends from Maryland 

 northwestward into northeastern Ohio and thence into southern Michi- 

 gan. The present northern boundary is approximately coextensive with 

 the northern outcrops of the Siluric strata of New York. Ontario, and 

 Michigan. The formation is thus seen to occupy an elongated basin, 

 comprising most of New York and Pennsylvania and much of Ontario 

 and Michigan, with extensions into Maryland on the cast and Ohio and 

 perhaps Indiana on the west. The deposits of this area consist of elastics 

 on the east and an alternation of elastics and chemical precipitates in the 

 form of rock-salt, gypsum, and anhydrite in the western area. The 

 elastics on the east are clearly derived from the Appalachian old land 

 still farther to the east, this being the only possible source of supply. 

 These elastics comprise two types. The lowest is a conglomerate, usually 

 made up of more or less well rounded quartz pebbles and quartz grains. 

 except in its easternmost extension, where pebbles of other material also 

 occur. This is the Shawangunk conglomerate, traceable along the north- 

 ern Appalachian front from south of Kingston to some distance below 

 the Schuylkill Gap in the Blue Mountain of Berks County, Pennsylvania, 

 near the Lebanon County line. Its westward extenl is unknown, as the 

 formation dips beneath younger strata and is not brought up again, nor 

 is it reached by wells, lis eastward extent has been traced to the Green 

 Pond-Skunnymunk Mountain region in northern New Jersey and New 

 York, where it is represented by \\w Green Bond conglomerate. The 

 conglomerate is practically everywhere succeeded by a red shale and 

 sandstone formation, which in the eastern section at Green Pond Moun- 

 tain is known as the Longwood shale. In the Helderbergs of New York 

 this formation, originally called Medina, has been renamed h\ Flartnagel 

 the High Palls shale from High Balls on the Bondoni River. In Penn- 

 sylvania the vct\ beds haw in the past generally been referred to the 

 Medina, though certain portions have been recognized as Salina under 



the name Rloomsburg shale. As will he more fully show ii in Hie detailed 



description, both (he conglomerates and Hie n^\ beds are thickest in the 

 easl and thin oul in all directions away from the source of supply. The 

 Beries is an almost exact repetition of the Bald Ragle-Juniata series, 

 deposition beginning with coarse pebble and sand beds and passing into 



