294 American Geologist. ^^y* ^9^5 
An unusually notable exposure of snail shells has been 
made at Fifteenth and Walnut streets, two blocks southwest of 
the cut which yielded the casts already mentioned. At a depth 
of about a foot beneath the surface on the summit of the bluff, 
at an elevation of i8o feet above, and directly overlooking, 
the flood-plain, numerous shells were uncovered. At not more 
than three feet enormous multitudes appeared and a perpendic- 
ular cut showed them to be scattered throughout its depth of 
twenty feet in incredible abundance. Since these twenty feet 
have been removed the quantity turned up by the plow or ex- 
posed by the scraper continues to be surprisingly great. Al- 
though there is a general distribution of the shells, the greatest 
numbers by far are conspicuously in pockets as is almost in- 
variably the case where they are remarkably numerous in pre- 
viously undisturbed upland loess. As is also usual, those in the 
pockets are crowded together in a manner clearly indicating 
that the arrangement was not voluntary; and generally a ma- 
jority of the shells are crushed into such a mixed mass as to 
prove beyond dispute that the crushing and burial were one 
combined act. Frequently the appearance of a shell indicates 
what surgeons call a "green fracture" suggestive that when 
crushed it was occupied by the animal, and this is verified by 
one of the fossil casts of the Sycamore street group. So far, 
only two casts have been discovered among the many shells ex- 
amined from the Walnut street exposure ; but since the numbers 
collected were comparatively very insignificant, a satisfactory 
statement in regard to casts is impossible, although two pre- 
serve the historical record as faithfully as more could do. Many 
of the large shells had the spire completely filled. None had 
the operculum preserved, and at only one other point has one 
been found. That was taken from the cut at the summit of 
King Eill soon after the erection of the water-tower. It was 
examined with keen interest because of the unusual occurrence 
of a shell perfectly closed by a disk of horny substance totally 
dissimilar from the calcareous shell. It was doubtless Helicina 
occulta. The unfortunate absolute ignorance of mollusks and 
consequent want of understanding of the value of the specimen 
resulted in its loss. A recent thorough search at the same 
place for another failed of its object but was rewarded with 
the cast of a Patula alternata partly enclosed in a remnant of 
