452 J. D. Dana— Geological relations of the 
) The limestones and associated slates of northwestern 
Westchester County are closely like those of western and 
southwestern Dutchess County in their semi-crystalline condi- 
tion and aspect, so closely, that, were the intervening Archean 
way, no one would suspect any difference of age or system. e 
southern. of these two regions looks, as regards its rocks, like 
an uninterrupted continuation of the northern. This resem- 
blance descends to details. For quartzyte occurs with the 
slightly crystalline limestone and slate of each, adjoining the 
Archean : as if precisely the same seashore work were then going 
on simultaneously on the north and south sides of the High- 
land peninsula now known as Putnam County. Further, some of 
age. 
: e evidence of Lower Silurian relations becomes the more 
remarkable the closer these are studied. In Dutchess County, 
in the Fishkill limestone belt, at points between Kast Fishkill 
(E, map, Plate VII) and Shenandoah Corners (8), the limestone 
is partly a white fine-grained variety, and partly a bluish gray 
scarcely crystalline rock; and the latter (at a place $ mile N. 
of Shenandoah Corners) afforded me (in an excursion made since 
the publication of my Dutchess County article) large shells, of 
a Strophomena, like S. alternata, distinct in form though dis- 
guised by pressure and slight alteration, indicating for the beds 
a Trenton age. A little to the south, between Shenandoah Cor- 
ners (S) and Hortentown (H), where the limestone extends up 
a valley, openings have been made for limonite and kaolin (as 
elsewhere along belts of Green Mountain limestone), and near 
Hortentown beds of quartzyte have been exposed in the exca- 
vations. The quartzyte (like that east of Matteawan, nearer 
the Hudson) lies between the limestone and the Archean. 
* This Journal, xvii, 386, 1879, and xx, 24, 214, 1880. 
