THE ZUNI SALT LAKE 193 



ments, including the fossiliferous limestone. By this means a great, 

 low mound of irregularly stratified material was built, extending from 

 the edge of the depression. Consequent upon this eruption, a 

 circular depressed area, a mile in diameter, subsided into the space 

 made by the solution of salt and in smaller measure by the ejection 

 of various rocks. 



A much less probable hypothesis is that not only the lava sheet 

 was extruded, but the sheet of volcanic ejecta was deposited and the 

 cones built up prior to the subsidence. If this was the case, there 

 is under the floor of the depression a sheet of lava overlain by a thick 

 mass of volcanic ejecta, faulted down from the level of the lava and 

 ejecta deposits on the rim. After the subsidence a new eruption 

 gave rise to the cinder cones, at least to the one with the crater, for 

 the other cone northeast may represent the stock of an earlier erup- 

 tion. Water has continued to rise in the bottom of the depression, 

 now only in small volume, but carrying much salt. Probably the 

 lake occupied the entire bottom of the depression at one time, but 

 evaporation and sediments especially those deposited by the tor- 

 rential water courses on the south side, have evidently diminished 

 the water area. 



