480 Scientific Intelligence. 
quartz-porphyry, diorites, and rarely in the andesite; some horn- 
deduced is as follows: Quartz-porphyry, earlier diabase, later 
diabase, earlier hornblende-andesite, augite-andesite, later horn- 
blende-andesite, basalt. The most abundant rocks are the ande- 
sites. The microscopic character of several of the rocks is illus- 
. trated on four plates of sections. : 
The “ propylite” of von Richthofen was proved to be an al- 
tered ek 
The rocks adjoining the lode are altered to great depths, and 
re often 
me- 
the iron coming from one of the iron-bearing silicates mong 
the results of weathering, freezing is stated to t une 
times conchoidal chips from the angles of andesite blocks to 
The quartz porphyry is deeply decomposed, and its porous struct- 
ure is said to be “perhaps due to the unequal contraction of the 
quartz and feldspar in cooling.” : . 
he changes along the lode are attributed to waters holding 
carbonic acid or alkaline sulphides, or other mineral ingrediony 
The conclusion is drawn, based on assays, of the rocks, agnee 
to be not altogether satisfactory, that the diabase, making t 
east wall of the vein (and now exposed for a length of 8,000 fee 
_ and gathered in the ores of the : 
_ tecks, “carbonates and alkaline sulphides would be formed, an — 
# 
