34 



PALEONTOLOGY OF NEW-YORK. 



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 bottopi ; 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 raade 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 tl^bottom, the ex- 

 panded fin would produce the dactyloid impression, M'hich 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, which 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 



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