REPORT OF THE DIRECTOR I915 9I 



Valleys." ^ The sand partings, as is observed elsewhere, have a 

 bearing upon the formation of some landslips. 



The clays are of fat, plastic nature and of bluish color except 

 in the upper beds, which have a brownish yellow tint from the 

 oxidation of the contained iron under weathering influences. The 

 division between the yellow and blue clay is sharp but not con- 

 stant as to depth, being in some places a few feet from the surface 

 and in others 30 or 40 feet; it is sometimes marked by the occur- 

 rence at this level of " clay-dogs " or calcareous concretions formed 

 by the leaching of the upper layers. The blue and yellow clays are 

 not very different in their chemical or physical properties, but the 

 former is usually a little higher in silica and alumina and lower in 

 the alkalis and alkaline earths than the latter, as it is also some- 

 what less plastic. Both are extensively employed in the making of 

 brick, in the molding of which they require from 25 to 30 per cent 

 of water to develop the proper degree of plasticity. 



The composition of the clays is indicated by the following 

 analyses of samples from the vicinity of Albany: 



I 2 



SiO^ 59-68 56.08 



AI2O3 i4-i6 15.36 



FeoOs 1.76 5-22 



Ti02 _ .90 .90 



CaO 6.68 7.20 



MgO 4-84 2.76 



K2O 2.75 3.19 



NaaO -40 1.47 



Moisture .65 1.16 



Ignition 7.75 7.90 



99.57 101.24 



Texturally, the clays are fine and soft, as the sand admixture 

 which arises from the clay partings is small in amount. A sample 

 from the recent landslip at Hudson showed 10.5 per cent of sand 

 and silt, the particles of which were all less than .1 mm in diameter. 

 The same clay after drying in the air bath absorbed 30.8 per cent 

 of water by weight before crumbling or slacking began, thereby 

 attaining the proper consistency for molding. Plasticity disap- 

 peared with the addition of 50 per cent of water, when the clay 

 became slightly fluent in the mass and no longer would hold its 

 form. With 75 per cent of water it was semifluid, slippery, 



1 N, Y, State Mus. Bui. 84, p. 175 et seq. 1905. 



