230 J. Barrel! — Upper Devonian Delta of the 



of the Upper Devonian of tlie Appalachian geosyncline, how- 

 ever, the sediments on the eastern outcrop are alluvial deposits 

 of rather uniform nature. They are dominantly siliceous sand- 

 stones, argillaceous sandstones, some conglomerates of fine, 

 well-worn gravel, and considerable shale. There is no sharp 

 change near the present margin. The sediments therefore 

 show no indication of an immediate source of erosion. If the 

 size and abundance of pebbles in what there are reasons to be- 

 lieve were once continuous alluvial deposits be used as a means 

 of estimating relative distances from the sources of erosion, it 

 is to be noted that in the Skunnemunk outlier the coarsest 

 pebbles of the conglomerate lie in the upper part of the for- 

 mation. They are well water-worn, of quartzite, showing much 

 previous transportation even here, and range from six to eight 

 inches in maximum diameter. The average pebbles are about 

 half this size. In the section of the Catskill rocks exposed 

 from the town of Catskill to the summit of High Peak, 3660 

 feet elevation, it is the portion at 2000 feet and above to the 

 mountain summit which shows notable conglomerate beds, the 

 pebbles commonly ranging from 1*5 to 2"5 inches in diameter. 

 The pebbles are largely quartzite. The southeastern outcrop 

 in Schuylkill County, Pennsylvania, is more dominanthy sandy, 

 less conglomeratic. The pebbles there are of vein quartz and 

 range from 0*5 to 1*5 inches in diameter. In the western out- 

 crops conglomerates are very thin and fine-grained, or wanting. 

 These observations are not along the same section and are 

 incomplete, but they show something of the rate of disappear- 

 ance of gravel at distances progressively greater from the 

 source of supply. They suggest that even the easternmost 

 outcrops are not close to that source. 



The outlier known as the Rensselaer plateau deserves sepa- 

 rate mention, although the age of the Rensselaer grit which 

 constitutes it is not positively known and is more likely Middle 

 rather than Upper Devonian. These sediments have been 

 described in the first part of this article (p. 448), the metamor- 

 phism and the relations to the Taconic Range in the second 

 part (p. 95). Although the sediments show by their character 

 and variety that they are nearer to the sources of erosion than 

 are those of the main area of the geosyncline, they do not show 

 that the present limits of the Rensselaer formation hold any 

 direct relation to the original boundary. 



The previous statements have referred to the continental 

 deposits of the eastern outcrops of the Upper Devonian. On 

 the northern side of the basin the present limiting outcrops 

 of both continental and marine nature show the principal rela- 

 tion in their sediments not to a nearby northern land but to 

 sediments from the southeast and to Appalachia beyond. The 



