Dikes of flic While fairer Jr/ocene. — t'rise. 251 
and it is easily recognized as identical with a la3'er (»f green 
sandstone lying near the base of the same beds, the Metamyn- 
odon sandstone of Wortman. In some cases it may be darker 
and softer from a larger mixture of clay, but never loses its 
distinctive sandy character. In the dikes of these beds and 
those below, the Titanotheriuni beds, one fact is especially no- 
ticeable, the contents of a dike at any point is universally 
from a stratum below. > 
The dikes commonly traverse the claj'S perpeiuiicularly to 
their stratification and in a straight line, but with no^common 
direction or any parallelism. They extend at least through 
the two lower beds, having here a vertical range of 450 feet. 
Ditf'erent dikes were traced continuously for over a mile and 
were uniformly about three inches thick; other dikes reached 
an observed thickness of a foot, and I was informed by Dr. 
Wortman of some IS to 20 inches wide. The thickness seemed 
to be constant in vertical range. 
" The strata on each side are undisturbed and only on the 
faces next the dike was there seen any evidence of motion. 
Here for perhaps a cpiarter of an inch in there was u ming- 
ling of the clays of different strata as if by water action, and 
a slight detiection upward. In some instances, at a point below 
the effect of surface wash, the sand Ijad penetrated the claj's 
for an inch or less on each side. There seems to he an entire 
lack of structure in the dikes such as is mentioned by Diller 
(Bull. Geol. 8oc. Am., vol. i, ]>, 425) and Hay (Bull. (Jeol. Soc. 
Am., vol. Ill, p. 58). 
In the cases where the dikes are connected with the chalce- 
dony crystals the veins nmy exist on one or both sides of the 
intruded material between it and the clay walls of the crack. 
The absence of the crystals from one side or the other is nf>t 
a local accident, but seems constant for large areas. In every 
case where it occurs, on one or f)oth sides of the core, the 
crystals have a perfect vein structure, presenting a tiat sur- 
face to the (!ore or dike and one to the clay wall, and meeting 
irregularly in the middle. There are inclusions in tiie veins 
identical with the substance of the dike and also of calcite. 
One noticeable fact is that the veins of chalcedony in many 
observed cases, and pnihably in all, thin nut fi-om aliove 
downward. 
