862 STUDIES FOR STUDENTS 



and soda-lime feldspars, a sprinkling of apatite and iron ores, 

 sporadic occurrences of an undetermined zeolite, and an extraor- 

 dinary number of minute zircons, which are mostly included in 

 the feldspars. The residual soil resulting from its decom])osi- 

 tion is highly plastic, of a deep red-brown color and has a dis- 

 tinct gritty feeling owing to the presence of quartz and unde- 

 composed silicates. Some 69 per cent, of this soil was found to 

 be soluble in dilute hydrochloric and sodium carbonate solutions. 

 It will be noted that 44.67 per cent, of the original matter has 

 disappeared, and that of the original silica 52.45 per cent, is lost, 

 while 85.65 per cent, of the iron and all the alumina and phos- 

 phoric acid remain. All the lime has disappeared; 83.52 per 

 cent, of the potash, 95.03 per cent, of the soda and 74.70 per 

 cent, of the magnesia are- likewise missing. The total amount of 

 water has increased very greatly, as was to be expected. The 

 calculation shows a small apparent gain in phosphoric acid, but 

 the amount of this constituent is so slight in the original rock 

 as to render it probable that this is due to errors of analysis. 



The elajolite syenite in the second series is a coarsely crys- 

 talline granular rock containing orthoclase feldspar in broadl}^ 

 tabular forms, accompanied by nepheline, biotite, pyroxene, 

 titanite and apatite, while fluorite, analcite, and thomsonite, 

 together with calcite, occur as secondary products. The rock 

 weathers away to a coarse gray gravel which ultimately yields 

 a clay from which may be obtained, by washing, a kaolin of a 

 fair degree of purity. The analyses are from the work of J. 

 Francis Williams.' 



The calculations show a much greater loss of silica than 

 in the ffneiss, a feature due, as will be noted later, to the absence 

 of free quartz in the syenitic rock. Attention should be called 

 to the fact that the soda has been carried away in greater pro- 

 portions than the potash. 



The diorite in the third series of analyses is, when fresh, a 

 compact fine-grained, almost coal-black rock, sometimes finely 

 speckled with white from the presence of feldspars. The micro- 



' Ann. Rep. State Geol. Survey of Arkansas, 1890, Volume II. 



