MARCELLUS SLATE OR SHALES. 181 



Another remarkable fart, niul wliich (uiglil not (o lie passed over without, reference, is 

 the absence in New-Yoric of the important mass of limestone known elsewhere as the 

 Mountain or Carboniferous limestone : its position is between the Chemung group and the 

 ■Old Red system or sandstone. The absence of this limestone has deprived the southern 

 tier of rounli(;s of an important rock, and which, if it had been deposited in its normal 

 position, would have changed the agricultural character of these comities. 



§ 2. Makcellus slatd: or shales. 



I have already stated that the upper part of the Onondaga limestone is charged with 

 black slialy matter ; that the rock itself is black from its presence, and that thin beds of 

 shale appear between the layers. Such then are the indications of change in the rock. 

 With the commencement of the black shale, the change appears complete. It is, however, 

 chemically a mere predominance of silico-argillaceous matter over the calcareous ; for most 

 of the rock, if not the whole of it, retains sufficient lime to effervesce with miner;il acids. 

 The lower part of the rock is more highly charged with lime liian the upper, and this fact 

 agrees with other circumstances that attended the deposition of the mass. 



The Marcellus slate or shales may be thus described : Rock a slate, thin-bedded and 

 fragile ; color black, and soils the fingers ; often exhales a bituminous odor when rubbed or 

 broken ; undergoes an exfoliation when wet, by which process it breaks down into soil : 

 calcareous matter disseminated throughout the rock. It would be impossible, from these 

 characters alone, to distinguish this rock from the Utica slate, the shaly portion of the 

 Trenton limestone, or the Genesee slate : its relations, and its fossils when its k lations are 

 concealed, furnish the only distinctive characters by which it may be known. 



This rock has excited attention in consequence of its color, and also by its containing a 

 small amount of coal : hence wherever its outcrop appears, numerous excavations have 

 been made, under the expectation of finding this valuable product. It is scarcely necessary 

 to say that all these attempts have failed : notwithstanding this, many persons are still 

 confident that they will succeed in finding coal, provided they had the means of pene- 

 ti'ating deep enough into the rock. 



Relations of the Marcellus slate. It reposes upon the corniferous portion of the Onondaga 

 limestone, from east to west, and along its southern outcrop, from New-Scotland in Albany 

 county, through Greene and Ulster counties, to Pennsylvania. Above, it passes into the 

 gritty and shaly portions of the Hamilton group. We have not yet been able to detect any 

 change in the relations of this rock in its prolongation westward. In this respect it is an 

 exception, as many at least of the rocks already described stand in connection with rocks 

 in the western counties which are unknown at the east. 



Places where this rock may he observed. The Helderberg range, which has become so 

 universally known for its fine display of rocks, may be visited for this purpose. It is, 

 however, concealed by its own as well as the debris of the succeeding rocks, in consequence 

 of its fragile character. Hence, in fields, or other places unwashed by creeks, its out- 



