TiiK Vr.M.\ .Mi".s.\ 



243 



grains. 'I'his incrustation and the tine silt and clay particles which 

 are often cemented are not broken down entirely by shaking with 

 ammonia. Under the microscope the sand grains have a rough- 

 ened appearance and as mentioned elsewhere, even the coarsest 

 separates effervesce strongly with acid. The roughened surface of 

 the sand grains probably accounts for the relatively high w^ater 

 holding capacity of this sand. The mechanical analysis of a few 

 typical samples of the tarnished sand are given in Table X. 



table; X — MECH.XNICAL ANALYSIS OF YUMA MEISA SOIL 



Nos. 6922, 6923, 6924 and 6925 are the same soils described 

 under chemical coraposition. 



No. 6942. Top foot of silt from the Colorado River water 

 mixed with sand as it occurs on the old Blaisdell Orchard. Cover 

 crops had been plowed under, but no recent manure had been ap- 

 plied. Orange roots were abundant in this layer half way between 

 the tree rows. 



No. 6943. So-called hardpan of gravelly sand with some lime 

 concretions; about one foot thick, occuring as sub-soil beneath 

 6942. 



No. 6944. Clean tarnished sand beneath 6943 ; containing few 

 orange roots probably due to insufficient irrigation to penetrate 

 the third foot. 



No. 6945. Virgin tarnished sand betw^een the old Blaisdell 

 Orchard and Hill's Orchard. A little lime was noticeable. 



No. 6946. Indurated sand with much lime from just outside 

 S. W. corner of Hill's Orchard. 



No. 6947. Surface from gravelly area between the Hill and 

 Hibbard places; immediately overlying the excessively limy sam- 

 ple 6948. 



