6oo WILLIAM J. MILLER 



the movements mostly took place much later, that is, since the 

 river has cut deeply into the distinctly dipping clay deposits so 

 that, under the action of gravity or gravity aided by earthquake 

 shocks, overlying beds have moved differentially over lower-level 

 beds in the general direction of the dip. In some local cases 

 differential movements within clays may possibly have been caused 

 by the crowding action of ice against upper portions of clay deposits 

 as explained later under another caption. 



A few examples of apparently similar intraformational clays 

 from other regions will be cited, with various explanations which 

 have been offered to account for them. In regard to corrugations 

 in clays near Boonville, New York, Vanuxem'' eighty years ago said: 

 "These interesting forms of disturbance were no doubt the result 

 of unequal, local, and lateral pressure." A very similar excellent 

 example of intraformational sand and clay in the Devil's Lake 

 region of Wisconsin is figured and described by Salisbury and 

 Atwood,^ who say: "The grounding of an iceberg on the surface 

 before the overlying layers were deposited, or the action of lake 

 ice, may have been responsible for the singular phenomenon." 



M. E. Wilson has described and figured^ interesting cases of 

 intraformational contorted and broken clays in Timiskaming 

 County, Quebec, and in regard to their origin he says: "Whatever 

 the cause of these peculiar deformational structures, it is evident 

 that they were contemporaneous with deposition, for the stratifica- 

 tion is uniform in both the overlying and underlying beds." 



In Albany County, New York, according to Nason, 



A layer of blue clay about a foot in thickness and one hundred feet long is 

 crumpled and gnarled, appearing as though its laminae had been disturbed by 

 some dragging or shoving weight, while above and below the layers are exactly 



parallel and whoUy undisturbed Bearing in mind the fact that the clay 



banks are vmderlain by sand, the water circulating through these sands gradually 

 undermines the clay bank and tilts it to such an angle that one part of a bed 

 would slide over the other, only leaving visible marks along the particular 

 stratum disturbed, and in the form of crumplings. Many of the clays lie at an 

 angle to the horizon, and only a slight tilt would suffice to give rise to a shp.4 



' L. Vanuxem, Geol. N.Y., Part 3 (1842), p. 215. 



2 Salisbury and Atwood, Jour. Geol., Vol. V (1897), p. 143. 



3 M. E. Wilson, Can. Geol. Surv., Mem. 103 (1918), p. 142 and Pis. 15-16. 



4 F. L. Nason, N.Y. State Mus. Rept. 47 (1893), p. 465. 



