Stevenson.] 



302 



[Aug. 15, 



detrital fragments become very coarse in the mountain region, just as they 

 do on the Youghiogheny and Oastleman's, and the deposit hears some re- 

 semblance to glacial debris. The huge fragments have been transported 

 but a short distance, and slides from the mountains are mingled with de- 

 tritus moved by the stream ; so that, upon the whole, the deposit has little 

 likeness to the material covering the terraces on the lower Monongahela or 

 youghiogheny, where the larger blocks have been rounded during their 

 long journey, while many of the smaller ones have been reduced to fine 

 sand or clay. 



II. 

 Resume of the Facts and their Relations. 

 Looking now at the observations recorded in the foregoing part of this 

 paper, we see that although very fragmentary, they show the existence of 

 two sets of benches, in one of which, the higher, the individuals have an 

 almost unvarying level, whereas in the other or lower set, the members 

 have no definite altitude with respect to tide, but vary much, as do the beds 

 of the streams along which they are found. Arranged in tabular form, we 

 have, first the benches of the higher series : 



1. Chestnut Ridge, Seaton road above tide, C580 feet. 



2. Chestnut " National road " 2400 " 



3. Top bench in Somerset county " 2323 " 



4. Middle bench of " " 2288 " 



5. Bottom " " " 2123 " 



6. Bench near Confluence " 1820 " 



7. Sixth bench near Loyalhanna " 1690 " 



8. Fifth bench " " " 1570 " 



9. Fourth " " " " 1520 " 



10. Third " " " also at 



Hillsborough and Beallsville " 1475 " 



11. National road, Washington county. . " 1445 " 



12. " " " . " 1420 " 



13. Second Loyalhanna bench, also Na- 



tional road near Beallsville and 



Hillsborough " 1380 " 



14. National road east from Brownsville " 1350 " 



15. Tenth bench of Stcwartstown series, " 1290 " 



16. Intermediate bench, Dunbar cr., 



Possum cr., Greensburg " 1270 " 



17. Ninth bench of Stewartstown series 



First Loyalhanna bench. ..above tide, 1225 to 1240 " 



18. Eighth bench of Stewartstown series, above tide, 1195 " 



19. Seventh " " " " 1130 " 



20. Sixth " " " " 1100 " 



The elevation of low water at Pittsburgh, as used by the City Survey- 

 or's office, is 699 feet above mean tide. 



