90 NEW YORK STATE MUSEUM 



seventy-five years. The larger ones have involved upwards of 

 100,000 cubic yards of earth. 



The study of the phenomena has a very practical side. Their 

 range of occurrence coincides with the fertile, thickly populated 

 districts, where they are often of serious consequence in regard to 

 building foundations. There is need of exercising due precaution 

 in selecting the sites for heavy structures, and also providing for 

 their security, if they are to be placed upon earth. Ordinarily it 

 is not a difficult matter to test the conditions that exist in any par- 

 ticular plot of ground, but the interpretation of the evidences 

 requires the consideration of many factors which are not readily 

 apparent. The changes of contour likely to occur through the hand 

 of man and the influence of possible climatic variations particularly 

 mUst be taken into account. 



In nearly all cases the primary cause of earth dislocations may 

 be ascribed to the presence of water in some portion of the beds. 

 Consequently it may be possible to control their occurrence, if 

 proper provision can be taken to regulate the flow of groundwater. 

 The superfiscial phases of disturbance, like slumping, creep and flow, 

 naturally, are the least difficult to deal with ; while those involving 

 a deeper source of instability present a more serious problem, to 

 be solved, if at all, on the basis of a thorough investigation of the 

 local conditions. 



Characters of the Hudson Valley Clays and Their Associates 



The clays of the Hudson valley consist of horizontal beds which 

 for the most part were laid down in the expanded waters that 

 occupied the valley in late Pleistocene time, and that are known as 

 Lake Albany. They have a vertical range of over 300 feet, of 

 which the lower part extends below sea level, but it is only in the 

 immediate vicinity of the river that they reach a thickness of much 

 over 100 feet. They are remarkably uniform and seldom are inter- 

 rupted by any considerable intercalations of other materials, 

 although there occur all through the beds minute, often paper-thin 

 partings of fine sand which lend the bedded appearance always ap- 

 parent when the clays are seen in cross section. These sand partings 

 mark original fluctuations of sedimentation, but just what signifi- 

 cance they may have with regard to time periods, if any, is not 

 known. A discussion of this feature, as well as of the conditions 

 under which the clays were probably deposited, will be found in 

 Woodworth's "Ancient Water Levels of the Champlain and Hudson 



