lO NEW YORK STATE MUSEUM 



These ridges have a north-south trend, separated by rather narrow 

 parallel valleys. The latter are floored usually by limestone 

 (Wappinger) which has a fine crystalline texture and is usually 

 magnesian. The ridges are made up of fissile schist or hard slate 

 (Hudson). Below the limestone a hard quartzite is exposed in 

 places. The succession consists of Cambrian and Ordovician sedi- 

 ments which have been squeezed into folds and more or less meta- 

 morphosed in the process, the limestone and quartzite being now 

 exposed through erosion of the overlying schists along the axes 

 of the folds. The structure is complicated by local faults. 



Iron ores and slate constitute the main items in the mineral 

 production of this province. Both limonite and siderite are present, 

 limonite being the commoner ore in most of the developed properties 

 but it is associated not infrequently with siderite and in some places 

 the latter mineral predominates. The deposits lie along the contact 

 of the limestone and schist, more rarely within the schist, and follow 

 the north-south valleys. The ores have been excavated mostly in 

 open pits which seldom attain a depth of over 150 feet. The 

 principal mine localities are in the valley that extends from Hillsdale, 

 Coltimbia county, south to Dover, Dutchess county, but there are 

 other occurrences in the vicinity of Fishkill and Clove, Dutchess 

 county, and siderite alone occurs in eastern Columbia county, just 

 south of the city of Hudson. Slate is quarried mainly in Washington 

 county in the northern section of the schist belt. The characteristic 

 product is red slate of Cambro-Ordovician age. There are occur- 

 rences of purple, green and black slates in that section; some roofing 

 slate has been obtained, also, in Rensselaer, Coltimbia and Dutchess 

 counties. 



Interior Paleozoic province. This covers the part of the State 

 south of the Adirondacks and north of the Highlands to the west 

 of the Hudson river. It is by far the largest province of all, having 

 quite one-half of the total area or around 25,000 square miles. In 

 topography it presents a great diversity, comprising several more 

 or less distinct physiographic units, but in its geological composition 

 and structure it is relatively simple and over great areas uniform. 



The formations are all sedimentary, ranging from the Potsdam 

 of the Upper Cambrian to the Olean conglomerate at the base of 

 the coal measures. They lie in approximately the same relative 

 position they occupied when first upraised above the sea, not dis- 

 located by extensive faults nor corrugated by folds, although they 

 have been involved in regional crustal movements and have been 

 deeply dissected by erosion. The formations consist of the usual 



