436 JULIEN 



Location of Cities Along the Occlusion Line. — Attention has 

 been called^ to the position of Baltimore, as well as of New 

 York, Philadelphia, Washington and Richmond, on the wide 

 belt of crystalline strata which follows the coast from Alabama 

 to Maine and beyond. To this the name of " tide-water gneiss " 

 has been applied, as forming the limit of tide- water in all the rivers 

 of the Middle States.^ It has been further shown in regard to our 

 eastern streams that " the fall line along the inner margin of the 

 Atlantic coastal plain of the United States is marked by impor- 

 tant cities on nearly every large river that crosses it," viz., Tren- 

 ton, Philadelphia, Richmond, Raleigh, Camden, Columbia and 

 Augusta.^ 



But there is a coincidence of wider application, complexity and 

 significance, in my opinion, in the belt of igneous occlusions 

 near the Atlantic and its crossing at certain points by large 

 rivers, with the location of cities along this coast. 



At Manhattan Island it has been established that the violent 

 folding of the schists and their extreme metamorphism are the 

 self-evident and exclusive results of mountain-making at a period 

 preceding the main Appalachian uplift. The necessary infer- 

 ence has been thus expressed : The ridges in neighborhood of 

 New York City, " though in the form of low well-rounded hills, 

 are as typical mountains, in a geographic sense, as are the peaks 

 and ridges of the Green Mountains. The difference is merely 

 that, in the vicissitudes of destruction, the former have been 

 lowered nearly to a lowland condition. They are mountains 

 reduced in elevation nearly to a sea level. If the rocks that 

 once covered the site of the City of New York could be re- 

 stored, they would rise into peaks rivalling the highest moun- 

 tains in the world." "* In the Piedmont plateau in Maryland 

 the evidence of enormous denudation of overlying masses has 

 led to the conclusion : " The region seems to represent the base- 

 level of erosion of an old mountain-range that has been elevated 

 perhaps the twentieth time, and is now again being eroded." ^ 



1 Williams, loc. cit., 13. 



^D. S. Martin, Trans. N. V. Acad, Sci., IV, 1885, 19. 



3W. M. Davis, Phys. Geog., 1898, 127. 



-•R. G. Tarr, Bull. Am. Geog. Soc, XXIX, 1897, 29. 



5\V. M. Davis, Bui/. Geol. Soc. Am., 11, 1891, 317. 



