191 



Liiirled out li'o feet of pumiceous tuff. These moxintains were still islauds 

 ill Cretaceous times, but their area then was much greater than formerly. 

 Ill this period the mountains seem to liaA-e been gradually rising until in 

 the Fort Union epoch great swamps covered the entire country, the sea 

 being oltliterated for a time. In these swamps vegetation was luxuriant, 

 and the vegetable matter laid down in them forms today, tfie coal fields 

 of nortli western New Mexico. At the close of the Fort UuTou epoch, there 

 was a' slow subsidence. The Puerco was deposited ont'Mf^'-IPort Union, 

 and then tlie Eocene on th-at. the whole series being conformable. Then 











there came a violent change. The whole country was elevated above the 

 sea, much faulted and broken up, and blocked basins on a grand scale 

 resulted. These depressions were the lakes of Pliocene times. Oue large 

 lake existed in the vicinity of Jemez. and another in the Rio Grand Valley. 

 The lake at Jemez was filled up with the Jemez marls by the tributaries 

 of the Jemez River: and the Rio (irande Lake was silted up witli the 

 Albuquerque marls, probably l)y tlie tributaries of the river which at 

 present occupies that valley. Wlien these lakes were almost filled, there 

 was a further re-elevation of the country, and the rivers at o;ice com- 

 menced to cut down their respective clianiu^Is: hut this deepening of their 



