14 TRANSACTIONS OF THE [ocr. 28, 
6. Cecum pulchellum. Stm. 
7. Mactra solidissima. Chem. 
8. Cyclocardia Novangliz. Morse. 
9. Modiola modiolus. Turton. 
10. Astarte quadrans. Gould. 
J1. Balanus porcatus, very numerous fragments. 
On the surface of the bank, in addition to species already 
enumerated, I collected two specimens of Crenella glandula Ad. 
As this shell is mentioned by Prof. Verrill as occurring in the 
lower bed, it is probable that the specimens in question be- 
longed to that stratum. 
Layers 3 and 4 are homologous with the stratified sand which 
forms the bluffs of the east and north shores and probably com- 
poses the whole island. The greensand is probably a con- 
stituent of the whole deposit, as it occurs everywhere in the 
bluffs within two miles of Sankaty Head and also at the town of 
Nantucket. 
In Macy’s History of Nantucket it is stated that shells have 
frequently been found in digging wells on the island. Prof. 
Verrill in discussing the probable origin of these beds states 
that the character of the fossils indicate a reduction in the tem- 
perature of the water of about 15° between the deposition of the 
lower and upper beds. He assumes that the lower and Serpula 
beds were formed in some shallow bay protected from the outer 
waters by a terrestrial barrier which was eventually removed 
and the cold outer waters flowing in, the Atlantic surf filled the 
bay with beach sand and broken shells. 
From my own study of the deposit in question, I am inclined 
to differ with Prof. Verrill to some extent, and I do so with less 
reluctance inasmuch as he has not examined the locality him- 
self. 
The appearance and character of the different beds give strong 
indications that they are largely composed of transported ma- 
terial, and are the work, to a certain extent, of swift currents. 
The sand of the lower shell bed is clayey and ferruginous, and 
contains pebbles ranging up to 1} inches in diameter. The shells, 
moreover, of Ostrea, Venus and Mya lie in all positions, the 
valves being often separated. This state of affairs is difficult to 
reconcile with Prof. Verrill’s generalization. If the clayey fer- 
ruginous sand were the bottom ofa sheltered bay, we have no 
means of accounting for the pebbles or the condition of the 
shells. If, on the other hand, it were a deposit subject to the 
action of waves, the clayey matter would have been washed from 
the sand. Apparently the conditions were such that the peb- 
