LOESS AND ADOBE 



321 



reason that it is still accumulating and has not been sufficiently 

 dissected by erosion to expose sections to any considerable 

 depth. Many of the valleys of the arid region have been filled 

 by it to a depth of 2000 or 3000 feet. In the larger valleys 

 there are rocky crests, called ''lost mountains," which project 

 above the broad level desert surface, which are in reality the 

 summits of precipitous mountains that have been almost com- 

 pletely buried beneath these recent accumulations. The pre- 

 vailing color of adobe is light buff to gray, excepting when 

 contaminated with organic matter. In its typical form it is so 

 fine as to be quite without grit when rubbed between the fingers. 

 When examined under the microscope, it is seen to be com- 

 posed of irregular unassorted flakes and grains, principally 

 quartz, but fragments of other minerals are also present. The 

 adobe of Salt Lake shows flocculent masses of amorphous matter, 

 which, when thoroughly disintegrated, are found to consist of 

 minute sharply angular fragments of quartz and feldspar with 

 much calcareous matter, and only rarely a shred of micaceous 

 or hornblendic material. In size the particles vary from those 

 too small for measurement up to .08 millimetre in diameter. 



The valuable characteristics of the adobe are its extreme fine- 

 ness, great depth, and wonderful fertility. 



Chemical Analyses of Adobe 



CONSTITITENTS 



Silica (Si02) .... 

 Alumina (AI2O3) . . . 

 Ferric oxide (FeaOg) . . 

 Manganese oxide (MnO) 



Lime (CaO) 



Magnesia (MgO) . . . 

 Potash (K2O) .... 



Soda (NaaO) 



Carbonic acid (CO2) . . 

 Phosphoric acid (P2O5) . 

 Sulphuric anhydride (SOs) 

 Chlorine (CI) .... 

 Water (H2O) .... 

 Organic matter .... 



99.72 % 



II 



66.69 % 



44 64% 



14.16 



13.19 



4.38 



6.12 



0.09 



0.13 



2.49 



13.91 



1.28 



2.96 



1.21 



1.71 



0.67 



0.59 



0.77 



8.65 



0.29 



0.94 



0.41 



0.64 



0.34 



0.14 



4.94 



3.84 



2.00 



3.43 



99.79% 



I. Adobe from Santa Te, New Mexico. II. Adobe from Port Wingate, 

 JSTew Mexico. 

 22 



