CLAYS OF NEW YORK 629 



currents which laid down the materials, sand being deposited when 

 the velocity of the cnrrent was swift and clay when the water was 

 qniet. 



All of the jSTew York clays are of sedimentary origin except 

 those occurring along the JSTew York-Connecticut border line near 

 Amenia and Sharon. 



Prospecting- and exploring 



In prospecting for clay the topography is often of much help. 

 In the northern and western portions of the state the clay is gen- 

 erally found in the bottoms of broad valleys. An example of this 

 is the Genesee valley. Again at other localities the clay is found 

 underlying terraces along the sides of the valleys, as in the Hud- 

 son valley and along Lake Champlain. Deposits of a similar char- 

 acter will be found along the Delaware and Susquehanna rivers. 

 A terrace however does not necessarily indicate the presence of 

 clay, for some of the Hudson valley terraces are underlain by till. 



On Long Island for example the clay is found almost entirely 

 along the north shore; it no doubt underlies most of the island, 

 but on the southern side there is in most instances such a cover- 

 ing of sand as to make it useless. The presence of clay can often 

 be detected in railroad cuttings, in the sides of gullies or ravines. 

 In many instances however the occurrence of clay is only sus- 

 pected; then borings must be made with an auger to determine its 

 presence. As a deposit of clay is seldom of uniform thickness 

 throughout its extent, a sufficient number of borings should be 

 made in order fully to determine this point; a bed of clay may be 

 40 feet deep at one point and thin out to 5 or 6 feet within a dis- 

 tance of 15 feet. The writer has seen several instances in which 

 expensive plants have been erected and come to a speedy end, sim- 

 ply because the clay gave out, whereas the disaster might have been 

 avoided by previous exploration. Another important point to de- 

 termine is the presence of sand for molding and tempering. Many 

 of the clays in this state can not be made into brick without the 



