THE NONMETALLIC MINERALS. 



335 



iron oxides, potash and soda, together with lime and magnesia in such 

 proportions that they vitrify readily, forming thus an impervious 

 glass over those portions of the ware to which they are applied. 



The following analyses show (I) the composition of a slip clay used 

 in pottery works in Akron, Ohio, and (II) one from Albany, New 

 York. (Specimen No. 53583, U.S.N.M.): 



The Albany clay is stated by Nason * to glaze at comparatively low 

 temperatures and to rarely crack or check. It occurs in a stratum 4 to 

 5 feet thick. It is used very extensively in the United States, and has 

 even been,, shipped to Germany and France. (See also Specimens 

 Nos. 53582, U.S.N.M., from Brimfield, Ohio; 53580, U.S.N.M., from 

 Rowley, Michigan, and 52985, 52995, U.S.N.M., from Meissen, Saxony.) 



The name adobe is given to a calcareous clay of a gray-brown or 

 yellowish color, very tine grained and porous, which is sufficiently 

 friable to crumble readily in the lingers, and yet has sufficient coher- 

 ency to stand for many years in the form of vertical escarpments, 

 without forming appreciable talus slopes. It is in common use through- 

 out Arizona, New Mexico, and Mexico proper for building material, the 

 dry adobe being first mixed with water, pressed in rough rectangular 

 wooden molds some 10 by 18 or more inches and 3 or 4 inches deep, 

 and then dried in the sun. In some cases chopped straw is mixed with 

 it to increase its tenacity. Buildings formed of this material endure for 

 generations and even centuries in these arid climates. The material of 

 the adobe is derived from the waste of the surrounding mountain slopes, 

 the disintegration being mainly mechanical. According to Prof. I. C. 

 Russell it is assorted and spread out over the valley bottoms by ephem- 

 eral streams. It consists of a great variety of minerals, among which 

 quartz is conspicuous. The chemical nature of the adobes vary widely, 

 as would naturally be expected, and as is shown in the following analyses 

 from Professor Russell's paper: 2 



1 Forty-seventh Annual Report of the State Geologist of New York, 1893, p. 468. 



2 Subaerial Deposits of North America, Geological Magazine, VI, 1889, pp. 289 and 

 342. 



