264 The American Geologist. May, i89o 
one great lake or in numerous small ones. There are some in- 
dications that the former is the case. Be this as it may, the 
fact remains that the drainage from the mountains was into 
water in the near neighborhood either in the form of small lakes 
or large bodies. When these lakes were partially filled and their 
barriers removed, as was the case I think at El Paso, where 
the Rio Grande has cut a gorge across a mountain chain, a 
system of drainage began to establish itself in the old lake 
bottoms. At this time the mountain drainage was well es- 
tablished while the plateau drainage was only begun. 
How far this plateau erosion had proceeded when the great 
New Mexican basalt period of late Tertiary times began it is dif- 
ficult to say ; but there are indications that the drainage was 
in a state of extreme youth. In several places beneath the 
lava I have found signs of sharp erosion such as is characteris- 
tic of young drainage. This is particularly well shown below 
Santa Fe on the Santa Fe creek, which in cutting the lava has 
revealed a narrow canon sloping to the south and now filled 
with lava. This Tertiary river channel not only shows on both 
sides of the Santa Fe creek ; but also several miles north of 
this point at a place plainly visible from the Texas, Santa Fe 
and Northern Railway. At this place, which is near the base of 
the mountains, there was considerable erosion before the flow of 
basalt began ; but further north, between Embudo and Baranca 
the early drainage was not marked and the Tertiary sands be- 
neath the lava are flat topped, level and only slightly disturbed 
by erosion. 
Where this basalt flowed from has, I believe, been a disputed 
point. Some hold that it may have flowed from great cracks 
in the earth, others from cones. Of the former theory there are 
no proofs in this section ; but, on the contrary there are many 
cones from which vast flows of lava poured forth. At "Volcano," 
near the Colorado line, on the Denver and Rio Grande Railway, 
is one of these old volcanic cones. On each side of the cone 
there is a great thickness of basalt : but the lava thins out on 
all sides and at Embudo, 60 miles south from the cone, it has 
a thickness of only twenty to thirty feet. Fifteen miles below 
Embudo the lava exists on the surface only in the form- of 
boulders. The basalt that flowed from this cone alone covers 
an area of 2000 miles that can be traced. There are numerous 
other cones in northern New Mexico from which similar large 
