46 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
east of the town. In the abundant outcrops south of Bitter creek it was 
seen to be made up of lenticular deposits, whose groups of oblique beds 
rapidly vary in thickness. Neighboring sandy strata frequently exhibit 
a lenticular and cross-bedded structure on a small scale, in strong con- 
trast to the even-bedded deposits of the paper shales, or cardboard shales 
as I should prefer to call them. In one exposure, a layer of sandy shale 
four feet thick has been obliquely cut out in a distance of eighteen feet, 
and the excavated space was filled in with innumerable little lenses and 
cross-beds. In another exposure, a series of somewhat concretionary, 
somewhat lenticular beds is cut out to a depth of two feet in a length 
of five, and the cavity is filled with rather even layers, followed by 
finely lenticular beds ; the surface of local unconformity has in this lat- 
ter instance a maximum dip of 30°. For a hundred feet or more over 
the sandstone bench, there are frequent alternations of gray cardboard 
shales with whitish calcareous and gray sandy layers, whose wasting 
outcrops supply the slopes with abundant slabs, large and small. The 
shales are of a remarkably even and continuous stratification, for which 
a lacustrine origin seems eminently appropriate, and a fluviatile origin 
on a broad flood-plain hardly less so; but the frequent alternations of 
the shales with layers of other kinds indicate equally frequent variations 
in the form or depth of the parent water-body, whatever it was. Some 
of the varying beds are greenish marls, with no distinct stratification in 
layers three or four feet thick. The sandstones are gray while in place, 
but weather brown as they creep down hill: some of the slabs show 
regular ripplemark, with crests from two to four inches apart ; others 
are unevenly rippled and pitted; many of the layers show fine cross- 
bedding ; a few contain rounded fragments of shale. Various samples 
are shown in Plate 7 B. Some of the calcareous beds have their layers 
separated by thin and variable clay partings which thicken up to a 
quarter or half inch, and then thin out in eight or ten inches. Other 
calcareous layers are seen, when weathered, to consist chiefly of fine 
pebbles well cemented, though this structure might not be suspected 
from a surface of fresh fracture: the constituent pebbles and grains, up 
to quarter or half an inch in diameter, are usually well rounded ; they 
are often soft and clayey. The best specimens of this kind were found 
in the bluff northeast of the town. Their resemblance to certain speci- 
mens of tepetate, brought by Mr. R. T. Hill from the arid southwest, 
is very striking. The continuity of stratification in these variable de- 
posits is noteworthy. Bands of lighter and darker color may be traced 
for several miles on the northern slopes of Bitter creek valley. On the 
