CLAYS OF NEW YORK 593 



down throiigli the valleys of tlie tributary streams, having a mnch. 

 greater velocity in their valleys than it would have after it turned 

 into the Hudson valley, and the checking of its velocity as it 

 reached the Hudson would cause the deposition of the greater part 

 of its load. A large stream rushing down the valley of the Fish- 

 kill would drop its burden specially below it, where we find them 

 heaviest as the flow of the water was toward the south. Again, 

 Peekskill would behave in a similar manner. 



A curious and interesting phenomenon is the crumpling of the 

 clay at many localities. This disturbance often extends through- 

 out the section, and has been ca.used by slips or pressure from 

 above, as when the clay is covered by a thick delta deposit. 

 Prof. R. P. Whitfield has told the writer of instances where the 

 clay layers had been disturbed to a depth of several feet from 

 the surface by the weight of boulders and large trees. In many 

 instances there occurs a crumpled strip of clay between layers 

 which are entirely undisturbed ; this has been actually observed 

 by the writer to have been caused by slipping of the clay. 



Clay concretions. These are of common occurrence, specially 

 in the yellow clay. They are of varying form and size. Many 

 of them have a cylindric hole in the center, which is lined with 

 carbonaceous material. The flat concretions are found parallel 

 to the layers of the clay, and in many instances at a depth from 

 the surface to which the roots penetrate. 



Those found at a greater depth did not have the central cylin- 

 dric cavity. They are very abundant in the yellow clay at 

 Haverstraw. Roots penetrating the clay at this locality were 

 surrounded by lumps of clay in the form of concentric rings. 

 These might seem to indicate the method of formation described 

 by Prof. J. D. Dana (Manual of geol. p. 628). Again in the 

 yellow clay near the surface at Coxsackie were found some forms 

 which were similar in appearance to what Dr J. I. ISTorthrup has 

 described as rhizomorphs.-^ They may be due to the roots which 



1 Trans. N. Y. acad. sci. 13 Oct. 1890. 



