zGo The American Geologist. October, isco 
lowstone park, which are in Tertiary rocks. Mr. Geo. F. 
Kunz reported siHcified trees near Carrizo, Arizona, projecting 
from volcanic ashe$ and lava, covered by sandstone to the 
depth of 20 or 30 feet. The species prevalent in Arizona be- 
long to the genus Araucaria, which has representatives in the 
south Pacific ocean which grow to the hight of 150 to 200 
feet. Some specimens, however, resemble red cedar. All, 
specimens show that the wood was undergoing decay before 
being petrified. On some specimens traces of fungi causing 
decay were found. These facts indicate a mild climate when 
the trees grew. The erect trees in the Yellowstone park be- 
long to the genus Cupressinoxylon. Some trunks rise only a 
few inches above the ground. Some are Sequoia. The largest 
trimk in the park is ten feet in diameter, and the highest trunk 
standing does not exceed 30 feet high. They are found near 
Lamar river, the finest exhibit being on Amethyst mount, and 
Specimen ridge, near, the road between jNlammoth hot springs 
and the town of Cooke, Montana. Yancey's fossil forest is 
one mile south of his hotel on the slope of a hill 1,000 feet 
above the valley. There are only two trees of considerable 
size, the largest stump being 15 feet high and 13 feet in circum- 
ference. The bark is not preserved, so that the true diameter 
cannot be ascertained. Recently 25 specimens of petrified 
wood were found at Three Tuns, Pennsylvania, in a disintegrat- 
ing sandstone with a feldspathic cement overlying the new red 
sandstone. 
."The most prominent theory to account for the petrifaction 
of these trees is that the trees in situ were buried by a cinder 
shower from an active volcano somewhat after the manner 
that Herculaneum and Pompeii were buried by ashes from 
\'esuvius. Showers of rain generally accompany volcanic 
eruptions and the finely divided cinders were swept down the 
slopes in the form a volcanic mud, which is called tufa when 
hardened. The tufa and cinders, it is supposed, covered the 
trees entirely. Afterwards hot alkaline waters passing- 
through the tufa and cinders dissolved out the silica, and when 
this water came in contact with the trees petrifaction began, 
each particle of woody matter being replaced by silica until 
the replacement was complete and the petrifaction finished." 
Silica in solution in alkaline water, whether rain water or 
oceanic water, readily replaces organic tissues, and other non- 
crystalline substances such as volcanic glass, or obsidian, and 
appears to be the prime agent in the production of many 
apobsidians. 
