PEBBLE-SWALLOWING ANIMALS. 
29 
The nearest place where the animal could have found such pebbles on 
the sea beaches must have been several hundred miles away from 
Ellsworth. We may conclude therefore that the Plesiosaurs were 
roving animals.” 
In a further letter, 1905 (accompanied by a capital photograph of 
Plesiosaur stones) Dr. Williston writes : “ Whether all pebbles in such 
bone-beds can be ascribed to marine organisms, I have considerable 
doubt, but that in many instances that is the real case I have little 
doubt. 
In the Cretaceous of Western Kansas there are, in isolated localities, 
thin bone-beds with numerous small rounded siliceous pebbles, inter- 
mingled wirh the remains of fishes and reptiles. To have ascribed 
their occurrence in such places to the carrying action of water seemed 
to me very improbable, since the neai-est land ?-egions of those times 
were several hundreds of miles away, and a continuous land connection 
is entirely out of the question. Nor could sea currents have carried 
them through such great distances. 
I had for that reason, long tiefore, reached practically the same con- 
clusion that you have, that they were the residue of the stomach 
contents of fishes and reptiles.” 
In 19041 Mr. Barnum Brown (American Museum of Natural 
History, New York) writes : “ During the summer of 1903 the writer 
collected fossils in the Niobrara Shales of South Dakota. In nearly 
every instance of Plesiosaurs a large number of siliceous stones were 
found associated with the bones, often embedded in the matrix en 
masse. In one specimen, in which the largest dorsal vertebiai were 
four inches in diameter, there were at least half a bushel of these 
stomach stones, ranging from the size of a walnut to four inches 
across . . . The conclusion seems evident that invertebrate 
animals (Baculites, Scaphites, &c.) formed a large part of the food of 
Plesiosaurs, and that in default of crushing teeth the breaking up of 
the food was effected by the aid of these stomach stones, the presence 
of which further implies a thick-walled gizzard-like arrangeinent in the 
alimentary canal.” 
THEORIES. 
The preceding evidence being ample for the subject, we can now 
consider the various theories which have been envolved to account for 
the presence of these pebbles. 
The first one is that of the fishei-men, that the stones are swallowed 
as “ ballast ” to enable the animal to swim lower in the water. This 
theory has a wide range, being held not only by the Sealers of Cape 
Colony, but also by the Cod-tishers of Newfoundland and other parts. 
However, as Dr. Harrison has demonstrated in his paper, this has no 
foundation, the so-called “ ballast bag ” being really the stomach, and 
further, the creature does not appear to be able to eject the stones 
when they are no longer required for “ ballast.” These two objections 
are sufficient to dispose of this idea, which is simply an ingenious but 
fallacious attempt to account for the stones in the animal’s interior. 
^ “Science,” Vol xx., p. 184. 
