Art, IX.] Herrick-Johnson, Geology of the Albuquerque Sheet. 233 
the addition is unobjectionable but the color desired may be 
secured by adding iron oxide in the form of one of the red 
earths on the market. The natural color of the best flood plain 
clays is a rather pretty “golden buff” but other clays in 
the same flat where thoroughly impregnated by alkali produce 
a white or creamy buff brick. One serious objection to all the 
brick burned from the valley clays grows out of the discolora- 
tion in burning. In those parts of the brick exposed to the air 
in drying or in a kiln a white crust or film is formed which 
gathers on the exposed surface in an irregular and most disfig- 
uring manner. Finger marks where pressure was brought to 
bear on the brick while wet will be discolored in the same way. 
The discoloration has ruined the sale of otherwise perfect brick 
for many years in the Rio Grande valley. The film has been 
supposed to be due to fumes in the kiln during burning but it is 
noticeable that the color is worse in pressed brick and that the 
brick exposed to rapid drying or to the moist vapors in the kiln 
are the most seriously affected. Where the brick are covered 
or protect each other the color is absent. Where brick have 
been made from the mesa marl, as has been attempted in igno- 
rance of the composition, the whole kiln will be affected. On 
the newly scraped clay beds the efflorescence appears in a few 
hours and in the neighborhood of the clay for white brick shal- 
low pools are saturated with saline and alkaline materials com- 
posed of chloride of sodium, chloride of potassium, sulphate of 
soda, sulphate of potassium (?), nitrate of potassium and cal- 
cium chloride (?). The nitre is quite abundant in some cases. The 
same difficulty has been encountered at Socorro where the brick 
are of excellent quality otherwise. The clay of the flood plain 
is tempered with from one third to two thirds sand, being an 
excess but apparently necessary in these cases. The heat is 
estimated by the kiln men at about 1200 degrees and they state 
that fusion takes place at about 1300 degrees. The addition of 
some good clay base would improve the product and such ma- 
terial would be found in the Cretaceous clays on the Rio Puerco 
or perhaps near Coyote canon. Kaolin such as is used at So- 
corro seems not to be within reach at Albuquerque. This ma- 
