REPORT OF THE DIRECTOR I915 97 



the building at this point seems to have prevented the sUde from 

 continuing down the slope with its first force, so that the many- 

 houses and a hospital in its path escaped destruction. The noise 

 from the disturbance was heard over the whole city. This again 

 seems to have been a slide of earth in more or less coherent con- 

 dition and not a flow. 



Albany. The terraces on which Albany is built have a rather 

 gentle slope toward the river in contrast with those on the east 

 bank. Few large slides have taken place within recent times, but 

 minor disturbances are common and have to be reckoned with in 

 building and engineering operations. In some of the older sections 

 the walls of buildings show a general settlement of the ground in 

 one direction which is perhaps referable to creep. 



The geological conditions in this vicinity are rather unusual, 

 as has been already noted. The rock walls of the Hudson gorge 

 are exposed north and south of the city in the first rise of ground, 

 but under Albany itself there appears to be a broad embayment 

 opening into the gorge at grade and extending west below the 

 terrace of Capitol hill. Its presence is concealed by morainal 

 gravels and bedded clays, and is inferred from test borings which 

 have been carried down to rock. How far this depression may 

 extend to the west has not been determined. It seems most likely 

 to mark the mouth of some preglacial stream channel and if so it 

 is probably the old outlet of the Mohawk now shifted 10 miles 

 to the north. 



The great depth of blue clay under Albany is an element of inse- 

 curity, accountable for most of the movements of ground that have 

 taken place from time to time. The clay attains a thickness of over 

 100 feet and its lower part is likely to be wet. It lies upon a thin 

 bed of till, below which is generally found water-saturated sand, 

 10 feet or so thick. As an example of the general conditions, 

 the following section from the site of the New York Telephone 

 Company's building on State street, below the Capitol, is shown : 



Blue clay , 103 feet 



Clay and gravel (till) 2 " 



Fine sand (water bearing) 9.5 " 



Medium sand 3.19 " 



Hardpan 1.06 " 



Bed rock (shale) 



The layer of till above the sand acts as a seal to the water which 

 may be under considerable hydraulic head. The basab part of 



