102 NEW YORK STATE MUSEUM 



The disturbed ground consisted of bedded blue and brown clays 

 of the normal Lake Albany type, with sands and silts distributed 

 unevenly over the top. The surface was quite level except for a 

 slight slope toward Claverack creek, and represented part of the 

 terrace flat which here is about 150 feet above tide. The accom- 

 panying cross section, prepared by R. W. Jones of the Museum 

 staff, shows the general situation. On the south the clay terrace 

 terminates abruptly against the steep edge of Becraft mountain, an 

 uneroded remnant of Siluric-Devonic limestones, only slightly dis- 

 turbed, which rest upon the upturned edges of the metamorphosed 

 Hudson river (Ordovicic shales). The limestones and the Pleis- 

 tocene clays form the basis of the cement mixture. The most 

 marked depression within the area previous to the slip was the 

 trench of Claverack creek, perhaps 7 or 8 feet deep and 50 feet wide, 

 the bank of which was about 120 feet above tidewater. The slope 

 from the base to the main buildings to the creek was 30 to 40 feet 

 in a distance of 300 feet or more, or about i in 10, but somewhat 

 irregular. 



The clays with the surface silts or sands have a thickness in this 

 part of from 75 to 100 feet. They rest upon morainal gravels of 

 considerable thickness, which in turn lie upon the uneven surface of 

 shale and, on the southern end, of limestone. The glacial gravels or 

 bottom moraine no doubt increase in thickness toward the side of 

 Becraft mountain and tend to smooth out the irregularities of the 

 rock contours. 



In its character, the slide was typical of the unbalanced-pressure 

 class in which equilibrium is sought by subsidence of the heavier 

 load and uplift of the lighter, the adjustment taking place through 

 a confined substratum of wet clay. The subsided area included the 

 section between the river and the line of break west of the latter ; 

 the break was' defined by a nearly vertical bank of the freshly- 

 fractured clays up to 20 feet high. This bank described a broad 

 curve open toward the creek, with its center about 225 feet from 

 the stream channel ; it was traceable for a distance of about 1200 

 feet. The vertical displacement amounted to 25 feet as a maximum, 

 and was greatest in the southern half of the belt, decreasing to 

 the north and also toward the creek. Along the creek itself the 

 conditions were reversed, the channel and the adjoining area to 

 the east being upraised, so that for a distance of 600 feet the former 

 bed was left high and dry and the waters above were ponded back 

 until a new channel could be opened through the clays. The new 

 channels follows a much straighter course, as it cuts off the bends 

 shown on the map. 



