94 The American Geologist. February, 1903. 
the area to the south of the Red Beds, it is quite possible that 
they did then exist, because the dip of the Carboniferous, and 
Red Bed strata have remained unchanged so far as direction of 
dip is concerned since the Red Bed revolution ; and the Jemez 
plateau has furnished a water supply for streams since even 
earlier times. The origin of these streams must, therefore, 
date back at least as far as the early Jurassic-Cretaceous or 
even earlier. 
Salt River. — This river has its source in the Puerco marls 
west of the Nacimiento mountains. Its channel is cut partly 
in the Fox Hills and partly in the Fort Union rocks. Near 
its confluence with the Jemez it follows the course of the fault 
north of the Mesa Blanco. Its age must antedate both Pleis- 
tocene and Pliocene times inasmuch as both series are found 
resting upon its valley floor. 
The Lower Jeines River. — In Pliocene times the upper 
tributaries of the Jemez together with the Salt river silted up 
the Jemez lake. The lake being filled, the various streams 
miited and cut a channel to the southeast to the Rio Grande 
embayment, which channel is here called the lower Jemez river 
or the river below Caiion de los Jemez. The age of this part 
of the river, therefore, dates from the earlier Post-Tertiary 
times. As the country was being rapidly elevated in Post-Ter- 
tiary times the river cut a deep, wide channel in the partly lith- 
ified Tertiary sands and clays. But its activity was suddenly 
arrested at the time of the Post-Tertiary volcanic disturbances 
Its channel was filled with lava near its confluence with the Rio 
Grande by the Bernalillo volcanoes as the remains of that lava' 
flow, in the old valley, show. At the time of this lava flow and 
immediately following it, the river bed in its lower course was 
elevated. A Pleistocene lake was thus formed ; and in it about 
100 feet of loose sands, gravels and clays were laid down. The 
lake remained in existence till an outlet was made through the 
lava barrier. The site of the lake then became dry, and has 
remained so to the present time. Since then the readjusting of 
the strata has elevated the old lake bottom on the north, thus 
causing the river to cut its channel deep in the loose Pleisto- 
cene. The stream in its lower course still has a considerable 
fall ; but, owing to the fact that its waters seep into the sand 
before reaching the Rio Grande, its flood plain is being built 
