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Cincinnati Society of Natural History. 



would be only by observing the gradual passage of the one into the other 

 that their true origin could be recognized. 



Sir Charles Lyell, (Principles of G-eology), has noticed in the Bay of 

 Fundy the tracks made on the' mud by various forms of animal life, and 

 has stated that these marks are often well preserved by the deposition of 

 mud by the tide. Many similar markings, made by different forms, have 

 been noticed in studying mud banks, and reference will here be made to 

 them in detail. 



Trails made by mollusks of various sorts are most abundant. That made 

 by a small lamellibranchiate shell (Cyclas) forms a series of semi-circles, 

 as if the animal, in moving, had wriggled along in a one-sided manner and 

 left its peculiar mark (Plate 8, figure 4). Still another, probably made by 

 a Melania, is a broad, winding, sinuous trail, depressed in the center and 

 elevated at the edges (Plate 8, figure 8). It is sometimes three feet in 

 length, and twists and turns in all imaginable directions. Sometimes it 

 ends abruptly, as if the animal had burrowed under ground and intended 

 to appear in another spot. 



Still another sort of trail, also probably made by a mollusk, turns and 

 twists on itself and forms a series of interwoven loops or circles (Plate 8, 

 figure 5). Still another sort forms a broad track, depressed in the center, 

 elevated at the edges and marked outside by a continuous series of small 

 depressions (Plate 8, figure 7). This is probably made by some sort of a 

 many-legged creature, such as the hard-cased worms which live in rotten 

 wood. Another trail is a long, sinuous line like the crenated edge of a leaf, 

 and is probably also made by a mollusk (Plate 8, figure 6). 



All these markings are very different from the true burrows, so common 

 on all mud banks. Some of these are long and continuous, branching here 

 and there, turning from side to side, or back on themselves, as it may hap- 

 pen. Those which have been noticed are made by beetles and a small 

 larva, and differ considerably in appearance. They assume at the same 

 time a different aspect, as they are covered or uncovered. In the first in- 

 stance a regular series of transverse lines, formed by the small particles of 

 mud thrown up in the course of the excavation by the insect, gives a reticu- 

 lated appearance to the burrow, as shown in Plate 9, figure 1 ; but when 

 this top is taken off, all the reticulations disappear, and there is left simply 

 a hollow, having the same general form as at first, but being plain on the 

 top and wider than before uncovered (Plate 9, figure 2). Unless it was 

 understood that the difference in appearance was thus caused, it might be 

 supposed that the two were the results of the work of different forms of 

 life. 



