/)i/,cs of f/ic White Hirer Mioeene. — C'usc. 258 
is shown by the perfect fusion of tlie veins of chalcedony in 
crossing each other. They were formed all at the same time 
in cracks which crossed each other. 
Hatcher (Am. Nat., March, 1893, pp., 20S, 209) says of these 
veins: "On first thought the writer was inclined to attribute 
their origin to mud cracks, any particular region where tliey 
now occur having been for short periods, during seasons 'of 
low water, above the water level, and subjected to the action 
of the atmosphere and the heat of the sun became baked and 
cracked; just as we now so often see at low water along tiie 
mud flats of our streams and lakes. But it is obvious that if 
these veins owe their origin to mud cracks they would be 
filled, not with chalcedony, but with the same materials as 
the overlying beds ; for when the waters again covered this 
region, the mud cracks would immediatelj^ be filled with the 
.same materials that now compose the overlying beds." This 
objection to the mud cracks, it seems to me, will hardly hold, 
as it is evident, in many cases at least, that the cracks were 
immediately filled by the intrusion of upward moving sand 
and water. 
Further, Hatcher says (loc. cit. p. 209) : "It has since oc- 
curred to the writer that these cracks were not made wliile 
the particular strata in which they now appear occupied the 
immediate bottom of the lake, but after the overljnng beds 
were deposited. The extreme fineness of tiie particles form- 
ing the clays of the Titanotherium beds in those places where 
these veins occur is evidence that the clays were deposited b}' 
a slow process of sedimentation in still waters. The bottom 
of a lake where such materials were being laid down would 
consist for several feet of a ver}- thin mud or ooze. This 
would gradually become firmer toward the bottom as deposi- 
tion continued, but would still mechanically retain a consid- 
erable per cent, of water. Later, when the entire overlj'ing 
series of strata were deposited and the region brougiit perma- 
nently above the water level, this imprisoned water would 
gradually disappear by filtration or otiierwise, aided perhaps 
by the pressure of ^he superincumbent beds. This loss of 
moisture in the clays would diminish their volume and bring 
about a readjustment of the particles composing them. The 
decrease in volume would be taken up in two ways: First, as 
