394 Haivcrth on the Arcka:an Geology of Missouri. 
numerous instances in which feldspar and other minerals have 
been partially fused by the basalt lava, and on cooling have had 
secondary rims attached which were oriented by the original crys- 
tals. They would thus be true secondary enlargements produced 
in precisely the way suggested above for the Missouri granites. 
In April of the same year E. Hussak,' in a paper entitled 
*'Ueber den Cordicrit in vulkanischen Auswiirflingen," describes 
the same kind of occurrences, in substance, as there mentioned by 
Bleibtreu. In 1SS4, C. Doelter and E. Hussak- published an ac- 
count of some very interesting experiments made by fusing dif- 
ferent kinds of natural volcanic rocks and observing the effect the 
fused mass had upon natural crystals of feldspar and other min- 
erals. Portions of the crystals were dissolved and, upon cooling, 
re-crystallized in the form of grains and lath-shaped crystals 
which were oriented by the original crystal, often grading into 
it in such a way that no w^ell defined line was left between the 
two. 
In 18S7 Dr. Alax Koch* described feldspar enlargements in 
kersantyte which he thinks could best be explained by attribut- 
ing them to secondary growths of the original crystals from the 
molten magma. 
Rosenbusch, in the last edition of his great work, vol. 11. p. 
341, mentions such enlargements in a general way, but gives 
no specific descriptions, and no references to the literature of the 
subject. On page 360 he mentions the work of Dr. Williams 
above given. Of course this kind of enlargement is entirely 
different from those in fragmental rocks described by Irving and 
Van Hise * for quartz, and by Van Hise^for orthoclase and horn- 
blende. 
Before describing topaz it will be well to speak of the changes 
which have taken place in the wall rock of the vein at the lo- 
cality known as the "Silver Mines." The vein itself extends 
from the west bank of the St. Francois, back in a south-west 
direction for an unknown distance. Years ago mining opera- 
1 Issued with above litle; also vol. 87 der Sitzb. der k. Akad. der Wis- 
senschaft, 188^. I. Abth. April Heft. 
2 Neues Jahrb., 1884. i Band, pp. 18-44. 
3 Jabrbuch der k. Preuss. geol. Landesanstalt, 1S87, pp. 77-78 and 98. 
« U. S. G. S. Bui. 8. . . 
* Am. J. Sci. vol. 30. pp. 233-235. 
