1/6 Bulletin of Laboratories of Deiiison University. [Voi. xi. 
territory because of the unusual simplicity of the geological fea- 
tures and the broad lines upon which they are expressed. There 
are no intricate problems of geological topography and the 
economic significance of slight deviations in contour is practi- 
cally nil. It has been decided that the present sheets will be 
sufficient for our immediate purpose and that whenever it seems 
best to undertake a more accurate delineation of the topography 
it will be desirable to employ a larger scale for portions of the 
sheet. 
The reason for the selection of this area lies primarily in the 
question of convenience. It would appear at first sight that it 
would be more profitable to undertake an area with more im- 
portant economic interests and, as a matter of fact, most of the 
work of the survey has been directed in such lines. But Albu- 
querque, as the largest city of the territory and the point from 
which our survey proceeds, seems to have a prior claim. More- 
over the very fact that in this region a large number of the im- 
portant geological problems are expressed in lowest terms makes 
it important that this area should be mapped and studied before 
attempting the presentation of the more difficult areas adjoining. 
This sheet is in a sense the key to the neighboring mining areas 
and the knowledge of this terraine is the foundation on which 
the later reports will be built. 
The sheet includes the area bounded by the meridians of 
io6° 30' and 107° west and the parallels of 35° and 35° 30' 
north, forming a rectangle of about 35 miles by 28.5 miles. 
This area of nearly a thousand square miles we have examined 
very minutely during the past three years but it must be con- 
fessed new facts of interest develop in each excursion. The 
broad outlines here laid down will require the work of years to 
fill in. 
No high mountains occupy this area but the fringes of 
three systems cross its borders. On the east rises the abrupt 
western escarpment of the Sandias and from the northern part 
of this range a spur of schist projects beyond the border. The 
great fault line which gave rise to the Sandias lies wholly to the 
east of the sheet and the knob of schists may be supposed to be 
