s Cc OTES No, 2 December 1977 Page 3 
THE FOSSIL SHELLS OF ROCKAWAY BEACH 
Morris K. Jacobson 
Alert shell collectors usually keep their eyes open for engineering 
dredging activities. These usually offer good opportunities for 
obtaining offshore species with little trouble. Such an opportunity 
came to me in Rockaway Beach, New York this year when huge quanti- 
ties of sand were pumped from about one mile offshore and deposited 
along the beaches, practically doubling them in width. I visited 
the dredging sites regularly but, in general, I was disappointed. 
I found huge quantities of fine white sand full of dead, discolored 
shells, all of them species I had been collecting on the beaches 
since 1938 when I first discovered the shell world. I was surprised 
that practically all the dredged specimens were in the same worn, 
weathered condition which I had been collecting. I was expecting a 
richer haul. Why so few live or newly dead specimens? Why almost 
only "“subfossil™ or fossil-looking specimens? This question was an- 
swered by my neighbor, Dr. David R. Franz, Professor of Biology at 
Brooklyn College. He pointed out to me that many of the species I 
had been collecting on the outer Rockaway Beaches were actually bay- 
living species, and not species normally found in the rougher water 
of the open sea. Such were, for example, Ilyanassa obsoleta, Nas- 
sarius trivittatus, Argopecten irradians, Crassostrea virginica, 
Mercenaria mercenaria, and the pulmonate Melampus bidentatus. Large 
fumbers of Specimens of all these species appeared on the ocean 
beach. I had noticed this earlier (see my articles on the shells 
of New York City in NAUTILUS, Vol. 56, pp. 139-144 and Vol. 57, pp. 
31-32, 1943). But I had assumed that these specimens had been liv- 
ing in Jamaica Bay, had been washed out to sea by the outgoing tide 
and had been swept back onto the outer beaches by the returning 
tides and waves. Dr. Franz quickly showed me that this idea was 
wrong. Many of the oyster shells, for example, were too bulky and 
heavy to be thus lightly wafted hither and yon, and the other speci- 
mens were far too weathered to have been recently killed and trans- 
ported. Besides, the tides didn't behave the way I thought they 
did. The truth is that these bay species had actually been depos- 
ited about 10,000 years ago, in the Holocene period just before the 
last Ice Age. 
At that time, instead of the ocean washing along the outer beaches 
of the Rockaways, as it does now, there was a large, shallow bay 
separated from the open seas by a barrier beach -- very much like 
Jamaica Bay is today, separated from the ocean by the Rockaway Pen- 
insula barrier beach. In this ancient shallow bay the bay species 
flourished. When the huge glaciers melted and the water level rose, 
the ancient Hudson River Delta -- now called the submarine Ambrose 
hannel -- was inundated by the sea. The bay-dwelling species died 
off and their shells were covered by numerous layers of ocean-depos- 
ited sand. And it is these ancient specimens, washed out subsequent- 
ly by underwater ocean currents and at present by the extensive 
dredging activities, which are scattered on the beaches. This means 
that the present day beach fauna of the Rockaways Sona Eee ae two 
elements: live ocean-dwelling species like Lunatia DErOsy pisula ” 
Solidissima etc., and fossil specimens of bay species which at pres- 
ent still live in Jamaica Bay. 
It is interesting that this offshore fossil bed contains several 
