52 G. F. Becker— Texture of Massive Rocks. 
some minerals before others (‘crystals of primary consolida- 
tion,’ as they are called. by Messrs. Fouqué and Michel Lévy), 
and the earliest of these crystals have good crystallographie de- 
velopment. Hruptive magmas thus obey a similar law to that 
observed experimentally in artificial fluids. It is usually ac- 
cepted that many of the crystals of primary consolidations are 
formed prior to the eruption of lavas; indeed I cannot remem- 
ber to have seen this denied, and yet it may be advisable to 
dwell somewhat upon the evidence of the fact. 
Darwin,* Mr. Clarence King + and others before them have 
observed that when smail branches are thrown out from lava 
streams of active volcanos and rapidly chilled, crystals of feld- 
spar and augite are found accumulated at the lower surface, 
while the upper portions consist of nearly pure isotropic glass. 
It is substantially certain that these crystals cannot have form- 
ed during the short interval elapsing between the rise of the 
material to the surface and the moment of complete consolida- 
tion. - Hence the crystals must have been suspended in the lava 
as it came to the surface and must have formed at a distance 
from the surface which is to be measured by miles. There is 
also other evidence nearly or quite as strong. Near the Com- 
stock I found (in a slide) a crystal of hornblende, bounded on 
all sides but one by sharp crystallographic outlines. 'The re- 
maining side appeared to represent a fractured or rather split 
surface, about one-half of the cross section of the prism being 
gone.t This fractured crystal is solidly imbedded in the 
groundmass of the rock, and the fracture must consequently 
have taken place while the groundmass was still fluid. It is 
almost or quite impossible to suppose any conditions under. 
which this crystal can have been broken excepting those attend- 
ing the actual rush of the lava from a profound depth to the 
surface. Hence it is as nearly certain as possible that this 
hornblende must have formed before eruption and under the 
pressure of miles of rock.§ The fact that “flow structure” is 
common immediately about porphyritic crystals in eruptive 
rocks, is by itself almost sufficient to show that the formation 
of these crystals antedates eruption. ‘The larger the crystals of 
primary consolidation the less probable it is that they were 
formed after the eruptionsof a porphyry. In the Washoe dis- 
trict there is an area of hornblende andesite in which the rock 
is studded with unusually large and very finely developed 
hornblendes.| An immense number of these are an inch and 
* Volcanic Islands, chap. VI. + Systematic Geology, p. 716. 
+ Geology of the Comstock Lode, p. 59 and Plate III. The double black bor- 
der shows clearly that the crystal must have been split. 
§ Others have also observed fractured or bent crystals in lavas. 
|| Geology of the Comstock Lode, p. 57. 
