30 
PEBBLE-SWALLOWING ANIMALS. 
The second theory is that the pebbles are swallowed by accident, 
that is, the animal in feeding on succulent material, such as sea- 
anemones, spawn, or other adhesive delicacy, might swallow any stones 
adhering thereto. This theory may account for a small portion, but 
stones taken in this manner would be of all sorts and varieties, both as 
regards composition and color, but this does not accord with the facts, 
for (as will be shown later on) the pebbles found are nearly all of a 
certain class, and singularly uniform in their nature, so that, while not 
denying that a small percentage may be attributed to accident, this 
cause is quite insufficient to account for the majority of those found. 
The third theory is that they are taken inadvertently, ^.e., by 
mistake. It is quite possible this may sometimes occur. We all know 
that wet pebbles frequently “ look nice,” and a young and silly fish or 
seal might be taken in by appearances and bolt a pebble or two, just as 
the human baby will swallow marbles and other indigestible trifles ! 
This would accord with the fact recorded by more than one observer, 
that seal pups have been .seen playing on the ice with pebbles, anrl they 
may occasionally swallow a few. But the same objection applies to 
this theory as to the previous one, that it only covers a small portion 
of the ground, and leaves the main question untouched. 
The fourth theory, which meets the facts better than any of the 
others, is that these stones were swallowed intentionally for the purpose 
of assisting digestion. In reviewing the evidence several important 
points stand out prominently. The first is that all the animals noted 
as addicted to this habit (both recent and fossil) were fish-eaters, that 
is, creatures which lived mainly or entirely on fish. The second point 
is that all of .them were either entirely or practically deficient in molars 
or crushing teeth. It is true the Seal family have molars, but (as 
pointed out by Dr. Harrison) they are mostly of a trenchant or chisel- 
like character, and more useful for cutting or separating than for 
grinding or masticating purposes. The third point is equally import- 
ant. A comparison of the pebbles found, whether in the rocks or 
recent animals, shows a remarkable similarity in general character. 
They are nearly all siliceous (quartz, quartzite, or kindred rock), a very 
small percentage being non-siliceous, and another peculiar feature is, 
they are nearly all white, or very light tints approaching white. 
Burther, they agree in shape, size, and general characteristics. Dr. 
Williston kindly sent an excellent photograph of Plesiosaur stones from 
Kansas, and when this is compared with the pebbles in the Rhsetic 
Bone-Beds, or in the recent Sea-lion’s stomach, the “ family likeness ” 
is undeniable. 
As regards the whiteness of the greater part of the pebbles, 
this is a remarkable feature, as in most pebble-beds or beaches 
white quartz pebbles are scarce, the great majority being dark or 
full-colored, exactly the reverse of the “ stomach stones.” This 
certainly indicates that these stones were purposely selected by 
the animals as being the most suitable for the purpose required, 
and that can only be as an aid to digestion. (As regards 
selection of material by animals, numerous cases are known, 
one which comes pretty close to this subject being the domestic fowl. 
