The stratified fossil-bearing rocks, of which alone we have 

 hitherto spoken, cover all the State of New- York, except the 

 southeastern corner from Newburgh and Fishkill to the sea, and 

 the Adirondack region comprising most of the country lying 

 between Lake Champlain and the Black river. These two por- 

 tions of the State exhibit rocks of a diiferent character. 



Next below the lowest of .the fossil-bearing rocks are generally 

 found a series of hard, semi-crystalline strata, of which gneiss is 

 the most common and conspicuous form ; though they embrace 

 many other varieties, such as the coarse gritty rock known as 

 mica-slate, and the coarse-grained crystalline white marble of 

 "Westchester county. These rocks are believed to have been 

 originally in most, if not all cases, sandstones, limestones and 

 slates, much like the fossil-bearing strata before described 

 (though generally older in age and lower in position), and to 

 have been exposed to the influence of subterranean heat and great 

 pressure in such intensity that their whole appearance has been 

 changed, and their materials so aJBfected as to suffer chemical 

 changes which have produced the coarse crystalline structure 

 which most of them present. The same cause must have oblite- 

 rated their fossils, if they ever contained any. Instances are 

 known in many places where the outbreak of a vein of lava, 

 trap, or some other melted mass from below, has cut through 

 stratified rocks, and the heat has changed them at the place of 

 contact so that black limestone becomes white crystalline marble, 

 sandstone becomes a close grained jaspery rock, and the fossils 

 of both are obliterated ; though at a short distance both these 

 rocks retain their usual appearance, and their fossils are distinct. 

 Such facts seem to prove fully that the class of rocks of which 

 we speak have been changed by heat from their original char- 

 acter, and they are therefore known as Metamorphic rocks, a 

 term derived from Greek words signifying " changed in form." 



These rocks seem almost everywhere to underlie the older 

 fossil-bearing strata, and appear where 'uplifts from below have 



