I. G. White — Bowlders at high altitudes. 379 



exceed an elevation of 1050 feet above tide are covered with 

 transported, or terrace material, but where the summits go 

 more than a few feet above that level we find no transported 

 material upon them, but simply the decomposed country rock. 



A fine example of one of these bowlder-covered divides may 

 be seen at the mouth of the Youghiogheny River, back of Mc- 

 Keesport, Pa. The "divide" in question is one between the 

 waters of Long Run, which puts into the Youghiogheny, two 

 miles above McKeesport, and that of another little stream 

 which heads up against it, and flows into the Monongahela 

 within the city limits. The divide between these two water- 

 ways, although 275 feet above the level of the river, is almost 

 imperceptible in a broad, and bowlder-covered valley through 

 which there is not the slightest doubt that the waters of the 

 Youghiogheny once flowed during the epoch of submergence. 



When we cross to the eastern side of the Alleghenies, bowl- 

 der beds are also found at high elevations along all the streams 

 which have their sources in the mountains. At Piedmont, on 

 the North Potomac, where water-level is about 910 feet above 

 tide the rounded bowlders cease at 150 feet above the stream, 

 while at Cumberland, 50 miles below, where the river level is 

 615 feet above tide the rounded bowlders can be traced up to 

 300 feet above the stream. 



That this region along the Potomac has been submerged 

 during recent times, seems fully proven by some facts observed 

 along Patterson's Creek, 8 miles below Cumberland ; for here 

 the submergence is attested by the presence of a bed of curious 

 conglomerate, made up of angular and water- worn fragments of 

 local rock (limestone, slate, sandstone, &c.) the cementing mate- 

 rial being lime and iron. The stratum is 1-3 feet thick, and the 

 remnants of it encircle the valley of the stream where it is found 

 10-15 feet above water level. It is reddish colored from iron 

 stains and would seem to correspond quite well with the " Bryn 

 Mawr " conglomerate described by Prof. H. Carvill Lewis, from 

 the vicinity of Philadelphia. It seems to have once covered 

 a considerable area in the Patterson's Creek valley, since Col. 

 Jno. A. Robinson, who first called my attention to the bed, in- 

 forms me that he has observed fragments of it five miles up the 

 Patterson's Creek valley. The elevation of the B. & O. R. R. 

 station at the mouth of Patterson's Creek is 568 feet above 

 tide, and the level of the conglomerate is 20 feet higher, or 

 588 feet above tide. 



A narrow, synclinal valley of Marcellus slate, bounded on 

 either side by arches (ridges) of Oriskany sandstone, which 

 carry on their slopes the outcrops of the Marcellus or Selins- 

 grove limestones, furnishes a sufficient reason for the origin of 

 this conglomerate in a submerged valley. 



