104 NEW YORK STATE MUSEUM 



honeycombed with worm borings which hardly would have been 

 the case if they had been subject to any considerable cutting by the 

 stream. 



The most important element in determining the character of 

 the slide, no doubt, was the saturated substratum of blue clay. 

 For some distance below the contact with the upper brown clay the 

 blue clay was thoroughly water-soaked, containing upwards of 

 50 per cent of water, and had become soft and greasy. It behaved 

 under the load of the higher ground exactly as a fluid, transmitting 

 the pressure horizontally and overcoming the resistance offered by 

 the thin crust of brown clay under the creek bed, which it lifted 

 bodily in the air, as already described. Test borings showed that 

 the condition of water saturation varied considerably from place to 

 place, and apparently the supply of water came not so much from 

 surface seepage as from lateral infiltration along the beds. The 

 extreme of wetness was encountered just beyond the northeast 

 point of Becraft mountain in near vicinity to the line of break, and 

 it would appear likely that there was an underground circulation of 

 water from that part of the mountain toward Claverack creek, 

 perhaps following a fissure or a brecciated zone in the limestones. 



The period immediately preceding the slide was one of unusually 

 heavy rainfall, the July precipitation, reported by the Albany 

 weather station, amounting to 5.05 inches. The wet zone was 

 doubtless raised above the normal level by the excess of rain, while 

 the thickness of the overlying coherent layer was by so much 

 diminished and the structure thereby weakened. 



The coherent brown clay which acted as a load upon the wet 

 substratum measured from 10 to 30 feet thick, increasing toward 

 the higher ground. To its weight should be added the artificial 

 load represented by the buildings and the stock pile of crushed 

 stone, this latter amounting to about 25,000 tons. Altogether, how- 

 ever, the artificial load was a mere fraction of the natural load 

 represented in the upper clay layers and to the writer hardly 

 appears to have been an appreciable factor in the precipitation of 

 the slide. 



Newburgh. The existence of early slides in the clay terraces of 

 this vicinity is inferred from the disturbed condition of the beds 

 revealed in some of the banks worked by the brick plants. Mather^ 

 mentions the occurrence of a fault at a point one-half or three- 

 fourths of a mile below the city on the river shore, made noticeable 



1 Geology of First District, p. 156. 1843. 



