58 RELATIONS OF THE TACONIC 



a rock of immense thickness. Wliere the siliceous band is wanting, the potsdam sandstone 

 passes by imperceptible grades into the calciferous, the calcareous matter gradually in- 

 creasing. The only view, then, which can be taken of these two masses, one of ■which 

 was invariably below the Calciferous sandstone, and the other below a grey slate near the 

 Primary schists in this section of country some twenty miles to the east, is that they are 

 totally (lifforont rocks, or belong to distinct eras ; and yet lithologically they are much the 

 same, and in position lie at the base of two distinct but successive systems. 



A few words more in regard to the Calciferous sandstone. This rock is sometimes asso- 

 ciated with a mass of compact blue limestone, more pure, though of a darker color, than 

 the common variety. It occupies a position usually inferior also to the common calciferous 

 sandstone. That it belongs to that rock, however, there can be no doubt, as it often 

 passes into it ; yet in some places it is exceedingly obscure in its relations. Its stratifica- 

 tion also is so imperfect, that it is impossible to decide with confidence whether it has any. 

 It is compact, though imperfectly jointed, and is always traversed by seams of white spar. 

 At one locality the blue mass beneath becomes incorporated with the grey mass above ; 

 but the layers on one side are marked by lines of deposit, which suddenly stop, and the 

 mass on the adjacent side is entirely destitute of planes of deposit. This locality is Gales- 

 ville, Washington county ; a locality, which all who doubt the soundness of my views 

 will do well to see and examine. They will here find the lower limestone resting, as at 

 many other places, upon a slate. 



The extension of the Calciferous sandrock east can not be marked by a continuous line : 

 it often seems to depend upon the amount of denudation and destruction the rocks have 

 suffered. I' appears too only in patches, and never in uninterrupted masses for any 

 distance. Generally in these instances it occupies the highest hills, or the knobs, and 

 occasionally extends down uj^on the eastern or northeastern sides. Whatever may be 

 its position, however, it is never interlnminated with the slates of the vicinity : it never 

 dips into, but reclines upon them. 



Mr. Hall, my colleague, is disposed to regard some of these masses of limestone as 

 appertaining to the Trenton. This view does not affect unfavorably the question whether 

 there is a system of rocks beneath the New-York system ; for at all those localities it is 

 clearly the oldest mass of this system, and it reposes unconformably upon a still older 

 deposit of slates. It hence matters not what name we give them : the fact has no ex- 

 ception. 



To the north, and perhaps the whole length of Lake Champlain, the Calciferous sand- 

 stone lies in a more continuous north and soutli line than in the immediate range of the 

 Hudson. From Whitehall south as far as the Southern highlands, we meet with it usually 

 in detached beds occupying the hills. Along this range is the great north and south frac- 

 ture, which has elevated these hills in a line almost continuous. The first effect of this 

 fracture and uplift was to produce a continuous ridge ; but subsequently the ridge was 

 broken through by diluvial currents, or else the lower points of the intervening strata were 



