HUDSON RIVER BRICK CLAYS.
The deposits of brick clay extend along both sides of the Hudson river more or less continuously from Sing Sing to Al bany, N. Y.
There are isolated patches below the former locality but they are not of any great extent. There are two narrow portions of the river from Staatsburgh to New Hamburgh, and from Corn wall to Jones' Point, where little clay is found.
The embankment in which the clay lies often rises steeply from the shore and the terrace which the clay underlies extends in some cases, especially along the upper portions of the river, one or more miles from the shore, while at other localities is not over 400 to 500 feet wide. In speaking of the terrace ex tending back several miles, it is not meant in an unbroken stretch, for numerous ridges of rock project above its surface at many localities.
The thickness of the clays is also very variable, they being underlain by irregular ridges of rock, and rounded hills of stratified drift or kames, or as at Verplanck and Cruger's, the clay lies in basins scooped out in the rock by the ice.
On the average, the clay is of good quality, and capable of producing a good brick. The Croton Point clays, and portions of those below Peekskill are very " fat." By a fat clay is meant one possessing great plasticity and being quite pure. Again, at other localities, as New Winsdor and Haverstraw, the clay contains numerous patches of quicksand. These patches are generally flat and lie parallel to the clay layers.
There is hardly a clay-bank, however, which does not show streaks of quicksand.
Two kinds of clay are found along the river, the blue and the yellow ; the former always underlies the latter, and occasionally they shade into each other or are interstratified.
As to the relative qualities of the two, the blue makes a better brick, and does not shrink so much in drying and burning as the yellow. The yellow gives a better colored brick, is tougher
than the blue, does not occur in as great quantity and is not as plastic. At some yards only the yellow is used ; at others, only the blue.
The Hudson river clays are, with few exceptions, situated so as to afford the greatest ease and economy of working. The yards are mostly located along the river front, the clay bank being adjacent to them, and at a higher level, so that the haul age of the clay is down grade to the tempering pits.
Though occurring usuallly in terraces, still the presence of a terrace does not always indicate clay. For instance, at Haver straw the clay is obtained from the sixty feet terrace, while the too feet one is composed of glacial drift and delta material. In prospecting for clay along the Hudson river there is little difficulty in detecting its presence. It can generally be seen on the face of the terrace escarpment, in road-cuttings, or in the sides of gullies made by small streams; which drain the ter race. In some cases the surface consists of sand or gravel, and then has to be pierced by the auger in order to determine the presence and the thickness of the clay. In determing the ex tent and thickness at any particular locality, it is of importance to make a number of borings, as sometimes the clay suddenly thins out. When the terrace is narrow the clay usually thins out as it recedes from the river. Unfortunately, as far as as certainable, few borings have been made in these clays to deter mine their thickness, and in most cases they have not been mined below the level of the yard, which is generally eight to ten feet above mean tide.