10 BULLETIN OF THE BUSSEY INSTITUTION. 
II. A sample of lighter colored rock from Dane’s Ledge, 
which had manifestly begun to decay somewhat. . . 93.282 0.202 
It has often been noticed by analysts,* that, as in the instance here 
given, the proportion of potash in a partially decomposed rock may be 
actually larger than it was in the original solid rock. The reason of this 
apparent increase is found in the fact that the soda, or rather the silicate 
of soda, with which the potash is associated in the rock, is often decom- 
posed and washed away much more readily than the potash silicate. 
Thus, Struve, as long ago as 1826, found among other things in a phono- 
lite from Rothenberg: — 
Silica. Alumina. Lime. Potash. Soda. 
In its natural condition . . 57.70% 22.80 1.05 3.45 9.70 
In its weathered condition . 67.98 18.93 0.86 5.44 3.26 
In a Basalt from Bohemia Sale p- 47) Struve found, — 
In the naturalrock. . . 1.35 7.35 
In the weathered rock. . . 2.62 2.31 
So, too, with rocks that, instead of having been exposed to the weather, 
have been partially decomposed with an acid. Thus, for example: — 
A. phonolite from Wisterschan, analyzed by Redtenbacher, in 1839, 
contained among other things, — 
Silica. Alumina, Lime. Potash. Soda. 
In the natural condition . . 54.35% 23.98 0.68 4.26 9.16 
In the part dissolved by acid. 41.22 29.24 1.03 3.56 12.11 
A phonolite from Marienburg, analyzed by Meyer in 1839, contained, 
In the natural condition . . 54.46 19.98 2722 9.17 2.67 
In the part dissolved by acid. 43.24 21.00 2.99 0.04. 7.11 
The fact is analogous to, and is probably of the same order with, the 
so-called fixing or absorptive power of soils; that is to say, the power of 
aluminous silicates, such as occur in the soil, to fix and hold potash 
rather than soda against solution and waste by leaching, as is explained 
in Johnson’s ‘* How Crops Feed,’’ New York, 1870, page 336 et seq. 
SANDS. AND Quartz Rocks. 
Quartz rock, with streaks of feldspar interspersed from 
Boston and Providence turnpike, West Dedham, Mass. 5.035 0.053 
Quartz rock, from granite quarry in Dracut, Mass., about 
14 miles from upper Lowell bridge on road to Nashua. 0.755 0.033 
Another specimen from the last-named locality. . . . 0.271 0.028 
Beach sand from Essex, Mass. A fine light-gray mica- 
ceous scouring sand, such as is sold by grocers for house- 
There is doubtless some ferric oxide in the rock, though I did not determine 
the amount. Special experiments are needed to determine what proportion of 
the sulphuric acid found by analysis may have existed as sulphur, in the form 
of pyrites, in the rock. 
* Compare, for example, Roth’s “Die Gesteins-Analysen,” Berlin, 1861, 
Article Phonolite, pages 22-24. 
