1883.] 485 [Wilds worth. 



American geology, and against it, so far as I am aware, no im- 

 portant arguments have ever been advanced. It provides, in the 

 first place, an adequate source for the Appalachian sediments. 

 It explains the absence of Paleozoic strata from the Atlantic sea- 

 board ; and renders intelligible the contours of the Gulf of 

 Maine. Finally, in the subsidence of this continent we have a 

 complete explanation of the structure of the Alleghany Moun- 

 tains. The pressure was entirely adequate for the work, it came 

 from the right direction, and was delivered at the right point, 

 namely, upon the eastern edge of the new sediments. 



If, as it seems necessary to believe, the folding and crushing of 

 the Paleozoic deposits was attended by the subsidence of an ad- 

 jacent portion of the crust, it is reasonable to suppose that the 

 subsidence was proportional to the crushing. Now the Appa- 

 lachian foldings and disturbance generally culminate in the Penn- 

 sylvania region; and it is both interesting and instructive to 

 observe that the Appalachian belt of crystalline rocks — the Pal- 

 eozoic land — is lowest and narrowest in eastern Pennsylvania 

 and New Jersey ; showing that the subsidence of the Atlantic 

 continent was most profound and extensive in this latitude, sub- 

 merging all but the actual shore line of the ancient land and 

 producing the great concave curve of the Atlantic coast line 

 between Cape Cod and Cape Hatteras. 



NOTES ON THE LITHOLOGY OF THE ISLAND OF JURA, 



SCOTLAND. 



BY M. E. WADSWOETH. 



This island, situated to the west of Scotland and south of the 

 Firth of Lorn, according to Macculloch, Murchison, Geikie, and 

 others, is composed of quartz rock and schists traversed by basaltic 

 dikes running northeast and southwest. The quartz rock occu- 

 pies most of the island particularly the western and central por- 

 tions, while the schists predominate on the eastern coast. The 

 quartz rock rises in the elevations known as the Paps of Jura to 

 the height of 2569 feet, and dips, according to Macculloch, 

 E. S .E., at an average angle of about '27°. 



