SURFACE DEPOSITS. 107 



composes is as secure as any other, yet it is everywhere easily 

 excavated with the spade alone. Notwithstanding this fact 

 it remains so unchanged by the atmosphere and frost, that 

 wells dug in it require to be walled only to a point just above 

 the water line; while the remainder stands so securely without 

 support of any kind, that the spade-marks remain visible 

 upon it for many years. Embankments also, upon the sides 

 of roads or other excavations, although they may be quite 

 perpendicular, stand for many years without change, and show 

 the names of ambitious carvers long after an ordinary bank 

 of earth would have softened and fallen away to a gentle 

 slope. Lime kilns, fashioned entirely out of this material, 

 even including the fire- arch, have been carved in the side of a 

 hill by* the spade, and used for burning lime during a whole 

 season or longer, without any interior or exterior wall or 

 other support, of any kind. Even potters' kilns have been 

 thus constructed and successfully used. For such purposes a 

 place is selected which is unusually dry, such as a narrow 

 ridge from which all water falling upon the surface is rapidly 

 drained away. In some instances small, temporary stables, 

 or cattle-shelters have been excavated in the side of steep 

 banks, and used for a few years, the roof standing with 

 considerable security in the form of an arch. Indeed so 

 securely does the material of this strange deposit remain when 

 excavations are made in it, and so easily is it excavated that 

 subterranean passages of many miles in length might readily 

 be constructed in it without meeting any impediment. Any 

 fortifications built upon these hills, which form a continuous 

 line along the greater part of the western border of Iowa, if 

 future emergencies should ever require them, might be readily 

 undermined by digging such subterranean passages ; and if 

 there were any cause or use for such works, catacombs might 

 be successfully constructed in any of them that would rival 

 those of ancient Rome. Beyond the influence of the atmos- 

 phere, they would probably endure as long as they. 



The peculiar property possessed by this material, of 

 standing unchanged in form when exposed to the weather, 



