34 
PALAEONTOLOGY OF NEW-YOKK. 
fishes. The question remains, then, whether fishes are capable of producing impressions upon 
the bed of the ocean ; and, if so produced, whether they can be preserved in the bed after the 
accumulation of successive depositions % In answer to the first question, I can only state that I 
have seen fishes driven into shallow water, and, in their attempts to swim, produce confused 
marks and scratches with their fins and tail, but presenting little regularity or definite form. 
That such markings could be preserved, we have no doubt, from the fact of the preservation of 
equally destructible markings made upon the ocean bed, and which are frequently found in a 
very perfect state. There may be some doubt whether fishes, in their undisturbed element, 
would swim so close to the bottom ; but still, in the search for food, they are compelled to do 
so.. The only explanation I can offer, therefore, is that these markings were made by the pec¬ 
toral, and perhaps the anal or other fins of the fishes, as they propelled themselves along the 
bottom of the sea. I do not doubt, from other evidence, also, that the water was exceedingly 
shallow, and probably disturbed by currents. The associated tracks and trails with other mark¬ 
ings, indicate very shallow water, or even exposed lines of beach, which may, however, have 
been very limited in extent, and not existing for any prolonged period of time. In expanding 
the fins and throwing them forward, no marked impression would be left; but as they were 
drawn backward and downward, the body of the fish resting on or near the bottom, the ex¬ 
panded fin would produce the dactyloid impression, which has three, four or five marks, as 
three or more rays reached the sand. In this we see an explanation for the little elevation of 
sand at the base of these impressions, which would naturally take place as the rays were drawn 
backward and constantly converging. In those impressions which present a simple imprint, it is 
probably due to a single spiny ray of the fin touching the sandy bed, and which, having the 
backward converging motion, produced the marks to be described. The mode of progression 
of fishes seems the only one by which we can explain this peculiar feature connected with the 
tracks. In this way, also, we can see why, in some places, the surface appears as if pressed by 
the body of the animal, and the tracks are confused as if he had floundered about, being unable 
to make rapid progress (See fig. 2, pi. 16). 
The difference in size and appearance of these tracks indicates that they were made by 
animals of different weight or size; and we have, in some instances, seen that in the same series 
the track varies from a single to a tridactyle impression. It should be recollected that the dif¬ 
ferent consistence of the sand would be sufficient to produce different impressions, even if made 
by the same animal. This is often clearly seen in the tracks of mice and other small animals over 
snow, winch in some parts is more compact than in others, and likewise in the tracks of similar 
animals upon sand. 
In attempting to decide what kind of animals have made these markings, we naturally recur 
to the fauna of the period. We find the Brachiopoda most abundant, Acephala and Gastero^ 
poda comparatively few, while the Cephalopoda are extremely rare. The crustaceans are not 
numerous, being far less so than in the following period. The remains of fishes, though ex¬ 
tremely rare, are sufficient to prove that they existed at this period, and perhaps in greater 
numbers than we are at present aware. It is not necessary, however, that the animals making 
