Coiigluiiicratc Dik'cs in So. Ariz. — Campbell. 137 
produced and then volcanic flows that conceal much of the 
older topography. The gravel hcds are semi-indurated and 
they attain a thickness of several hundred feet, but they are 
composed of andesitic material, or of gravel derived from the 
erosion of the Tertiary lavas and consequently they do not in 
an\- respect resemble the underlying Cretaceous conglomerate. 
The dikes were called to the attention of the writer by Mr. 
N. H. Mellor of Dudlcyville, who has made quite an exhaust- 
ive study of the geology of the region. Two such dikes were 
seen, and the writer was assured that others of similar charac- 
ter are to be found in the region. One of the dikes cuts the 
andesyte in a deep part of the liasin on Asli creek, about one 
mile above the camp of the Saddle Mountain Mining Company. 
This is a small dike ranging from two inches to ten or twelve 
inches in thickness. It cuts the andesyte at an angle of about 
seventy-fave degrees, and the rock, for a distance of a few feet 
on either side shows parallel cleavage planes as if there had 
been considerable movement connected with the formation of 
the fissure. The dike is a conglomerate composed of the same 
material as the great conglomerate bed at the base of the ande- 
syte, but only the smaller pebbles are present. Limestone peb- 
bles, having a thickness of at least two inches, were seen in this 
dike and granite and quartzyte pebbles of a like size are also 
of common occurrence. 
The other dike shows in a small ravine just south of Saddle 
mountain, and a photograph of its outcrop is reproduced in 
Figure 2. As may be seen in that figure, it dips at an angle 
of about sixty degrees and is of varying thickness, ranging 
from nearly a foot at the bottom of the ravine to only a few 
inches at the top of the slope where it branches, as shown in the 
upper parts of the view. As shown in the cut it is a conglom- 
erate composed of pebbles of limestone, quartzyte and igneous 
rocks. One of these boulders, showing in the photograph, has 
a diameter of four or five inches. 
The material composing both dikes is the same as that of 
the underlying conglomerate previously described, and since it 
is the only bed of this character, it is reasonably certain that 
the material was either- forced up along lines of fracture, or 
flowed up in an open fissure under strong hydrostatic pressure. 
With the evidence at hand it is impossible to say definitely how 
