THE MINING AND QUARRY INDUSTRY I914 2.J 



clays have been reported from only a few localities, the largest 

 deposits being found in the Hudson valley. The clay beds of this 

 area cover a section extending along both banks of the river for a 

 distance of about 40 miles south of the city of Troy. Not all the 

 clays in the area are slip clays. 



The clays found in the Hudson valley were deposited in the 

 waters of Lake Albany, a glacial lake which at one time occupied 

 a section of the valley from Rhinecliff north to the Battenkill. The 

 clays are underlain mostly by soft gray and black shales and sand- 

 stones of Ordovicic age. The grinding action of the ice reduced the 

 surface portions of the shales to a very fine condition and the 

 material then was carried by the waters from the melting glacier 

 into the lake where they were deposited to form beds of clay more 

 or less free from sand and gravel. The sediments deposited in the 

 lower section of the valley and from Troy north carry a larger 

 quantity of sand and also are considerably higher in alumina than 

 those in the middle section where the sediments were deposited in 

 the more quiet waters of the lake. The clays later were subjected 

 to the action of circulating waters which lowered the percentage 

 of calcium, magnesium, sodium and potassium in the surface layers 

 and resulted in the formation of a brown or yellow clay that 

 reaches an extreme thickness of 40 or 50 feet. The line between 

 the yellow and unaltered blue clay is very sharp. In one or two 

 localities the beds of yellow or brown clay are absent, the section 

 consisting of from 4 to 10 feet of bluish fine-grained sand usually 

 underlying a bed of yellow medium-grained sand. This bluish sand 

 is so finely comminuted that 95 per cent will pass a 100-mesh screen. 

 The sand grains retained on the 40-mesh and 60-mesh screens 

 consist of angular fragments of limestone with a few scattered 

 grains of clear quartz. Those retained on the 80-mesh and 100-mesh 

 consist almost entirely of colorless or iron-stained grains of quartz 

 with a few scattered grains of limestone and undecomposed shale 

 or slate. Following these sand layers there is an average of 20 

 feet of alternating thin layers of fine-grained blue or purple plastic 

 clay and very thin layers of blue or gray sand. Below this comes 

 the true slip clay. This consists of beds of blue very plastic clay 

 alternating with thin layers of sand. In other places the succes- 

 sions from the surface is fine sand, yellow clay and blue clay. The 

 lower layers of the slip clay are sometimes found with a thickness 

 of as much as 6 feet, free from sand. The chemical change due to 

 circulating waters has in no case reached a greater depth than the 



