302 The American Geologist. November, 1003. 
Francisco mountains, was encountered at several places in 
the Pleasant valley district on Cherry creek. After the rhy- 
olytes and trachytes of the region were ejected, the country 
suffered denudation for a time, followed by deposition to 
an extent that when the first sanidin-doleryte lava flow oc- 
curred its lavas flowed over an aggraded plain. Another 
period of erosion then commenced and continued till the rivers 
of the region had cut their channels to their present level. 
At this time a second lava flow occurred, followed by another 
period of erosion which lasted till the rivers had removed the 
lavas from their channels. Then the volcanoes in the vicinity 
of Green's point ejected a stream of lava into the North Fork 
of White river which flowed down the stream nearly to Salt 
river, as has been stated on a previous page. 
The lavas from these flows were ejected from the dikes and 
volcanoes in the White Mountain region, and from the vol- 
canoes in the vicinity of Green's point, and along the Kelley 
dikes and in the Nantan plateau. These lavas in habit and 
color are identical with those of the basaltic family. They 
spread in broad, sometimes thin sheets, are vesicular, the cav- 
ities being usually large and the partitions which separate them 
thick. In typical specimens the matrix is dark iron gray, and 
the imbedded feldspars are sanidin, sometimes a half inch 
in diameter. These lavas are further distinguished by grad- 
uation, through a change of matrix, into a true trachyte (Gil- 
bert). Moreover, these lavas were found to inclose limestone 
particles in the amygdaloid spaces which undoubtedly were 
taken up during the act of protrusion. To use the words of 
Mr. Loevv : 
"No chemist will admit that the lime was contained in basalt before 
its ejection since it would have been combined with the silicic acid of 
the molten mass and the carbonic acid liberated. Neither is there any 
foundation for the hypothesis that this carbonate of lime was deposited 
by infiltration ; to a close observer this appears quite an impossibility. 
At places where observed, (Sierra del Gila, Rio San Carlos, Camp 
Apache) its presence could be traced without any difficulty to the strata 
of limestone that had to be burst by the protruding volcanic material. 
The limestone broken into fragments by the concussion and heat of the 
molten mass fell in small particles upon and became entagled by it. The 
heat, however, liberated part of the carbonic acid of these limestone 
particles, and formed a bubble that could not escape, the mass assum- 
ing a thicker consistency after its ejection. The pressure prevented the 
