334 The American Geologist. June, i89o 
a durable stone; the quartz grains are generally small, bound 
together by a siliceous cement sometimes containing iron, col- 
oring the stone in all shades of yellow, brown and red. The 
rock is eas}^ to work with hammer and chisel, and very suita- 
ble for architectural ornamentation. Examinations in quarry 
and buildings prove that the rock well withstands the various in- 
fluences of this climate. The sandstone constituting the base 
of the Cretacic is generally less desirable, being softer and 
containing a calcareous cement. Both formations furnish a 
good limestone, often semi-crystalline and variously colored. 
On account of its hardness the stone is generall}^ selected for 
rubble masonry. 
Quicldime. — An excellent quality of lime may be obtained 
by burning the limestone of either formation. 
CeTTient. — The raw material for its product, a mixture of 
clay, sand, and lime, is found in abundance, which if burned 
will make cement of good quality. 
Clay — Underlies the river valleys. These deposits are var- 
iously colored, red, blue and yellow. Suitable for the manu- 
facture of Terra-Cotta, Majolica and pottery. 
Irrigation. — The method of irrigating the river bottoms has 
been practiced since the settlement of this country commenc- 
ed, almost 15 years ago. The average fall of the rivers and 
creeks is 10 feet per mile, and a low dam, from 5 to 10 feet, is 
generally sufficient to raise the water to the level of the land 
and permit, at low expenditure, irrigation of large tracts of 
fertile valley land. At the present there are about 16,000 acres 
under irrigation principally located on Dove creek, Spring creek 
South Concho and North Concho rivers. The lower uplands, 
covered with a rich marly soil, can be irrigated by constructing 
reservoirs. The land is gently sloping along the course of the 
rivers. Clay underlies the large undulating flats, and the ma- 
terial of the hills is a hard limestone clay and sandstone. The 
rainfall of the country is sufficient to keep even the largest 
reservoirs filled during the year, and the cost would be but a 
trifle in comparison with the benefits derived from such an 
enterprise. 
Grasses. — The principal varieties are : Oat top, which is eas- 
ily recognized by its reddish color. Though resembling the 
common sedge grass it is not as coarse and is well liked by 
stock. Mesquite grass, is of a light green color, growing 
