342 Tlie Americaji Geologist. June, i9co 
ramie, though the species, so far as known, are not Laramie 
plants and the Hgnites are followed by marine (Fox Hills) 
shells in great abundance. 
The Datil and Gallina ranges are composed of trachyte 
and rhyolyte intrusives of the same age as those of Bear 
mountain and the western flows of the Magdalenas. 
Ascending the Alamosa to a point north of the Datil, the 
dip increases and brings the red series to the surface. Im- 
mediately north of the Datil mountains is a large plain cov- 
ered with a loose brownish-red sandstone the age of which 
is conjectural. It appears to have been derived from detritus 
from the range and is probably Tertiary. From the western 
extremitv of the Datils is a most remarkable dyke of basalt 
or doleryte ten or fifteen feet thick, which extends as far as 
eye can reach in a direction somewhat west of north. Passing 
west, the country becomes a vast sparsely-wooded plain. In 
about range 13 is a second north and south dyke like the one 
above mentioned. The country rock, so far as exposed, is a 
white shaly sandstone which may possibly be Cretaceous. In 
the barren plain lying west of this dyke marl is the surface 
.stratum till the valley of the Mangoes is reached. Here we 
again enter the region of the red series and gypsum at the 
top of the characteristic Permian red beds appears in the 
blufifs below Ouemado. About eight miles down the valley 
from Rito Ouemado the valley has at some time been 
dammed bv a flow of basalt which extends both to the east 
and the west in an extensive sheet. The stream has cut for it- 
self a narrow passage through the dyke, and here is the site 
for a large reservoir that would irrigate an extensive region 
below. Very little expense would thus reclaim a large area. 
Only a short distance north of this place is a remarkable 
fault which passes across the valley in a north-easterly direc- 
tion and serves to bring the Cretaceous on the north in juxta- 
position with the red beds on the south along a line easily 
traced by the eye at a distance. Frequent lava cones are 
characteristic of this entire region, but our route to the north- 
west is over rather rolling country with hills in which the Fox 
Hill Cretaceous appears. Small lakes of storm water are 
scattered over the land in depressions lined with shale. Roads 
converge toward a slight elevation and the country is marked 
