33 



Hills above valley 300 to 400 feet- 

 Yellow banks 7250 '" 



Fainted caves 900 " 



Crossing of Devil's river 850 "• 



Prairie South, on road, highest points. . . . 110 to 1200 "- 



San Felipe spring 900 ' ^ 



Mud creek 1100 ' ' 



Fort Clark 1200 '• 



Nueces 860 '^ 



Uvalde 850 "• 



Castroville 630 "• 



San Antonio 550 "■ 



New Braunfels 565 ' ' 



Mountain City, Hays county 900 ' - 



HYDRAULIC CEMENT. , 



A here are many impure limestones in Texas which can 

 be made into hydraulic cements of more or less efHciency. 

 Argillacefous limestones yield hydraulic lime immediately 

 on burning. Such limestones must contain at least from. 

 ten to twelve per cent, of clay. Cements made from such 

 rocks require about twenty days to harden under water or 

 in moist places. Cements made from limerocks having- 

 twenty or twenty-five per cent, of clay set in two or three- 

 days ; and those having thirty per cent, harden in a fe^v" 

 hours. This last form of lime is sometimes called Romaiii 

 cement. 



However, every neighborhood which has good limerock 

 and clay lias all the elements necessary to make a good 

 hydraulic cement. These artificial cements are now exten- 

 sively made in Europe and America. 



Artificial hydraulic limes were used in a majority of the- 

 buildings in Paris, France, where hydraulic lime is made 

 by using four parts of chalk and one part of clay, all frem. 

 Mendon, a few miles from the city. The clay and chalfe 

 are ground by large wheels revolving in a circular track, 

 made into a paste and formed into bricks, which are dried 

 in the sun, and burnt like hydraulic limestones. 



The burning of hydraulic limestone requires peculiar 

 care, because, if the temperature be too great, the silex of 

 the clay is melted, and forms a too close combination with 

 the lime, and then it will not form a new compound and 

 make a good cement bj"- the addition of water ; hence, the- 



3 



