546 PROCEEDINGS OF THE ACADEMY OF [NOV., 



which will be found figured in the "Ichnology," are very similar to 

 the trails left by a piece of seaweed rolled along the bottom by the 

 advancing or receding tide. I watched this movement of tufts of 

 Fucus ve'sciculosus L., many times and the impressions formed 

 certainly bear a very close resemblance to many of the forms de- 

 scribed and figured by Hitchcock. 



These tufts are the ends of fronds, pieces varying from four or 

 five inches up to eight or ten inches in length, more or less conical 

 in general outline and in all cases broader at the outer end of the 

 frond than at the stem end. The advancing tide rolls them over and 

 over, generally more or less in a curved line, due to the somewhat 

 conical or pear shape of the tuft. The stem end thus touches from 

 time to time and makes a series of irregular impressions, somewhat 

 removed from the main line of impressions of the fruiting ends of 

 the frond. The marks made by the stem are deeper, but smaller 

 than those made by the fruiting terminations of the branches 

 These fruiting tips of the branches are bifid or trifid as well as simple,, 

 conical, bladder-like expansions and they sometimes make impres- 

 sions that simulate the tracks of three-toed reptiles or other animal 

 tracks. They look, however, as though only one foot were touching, 

 as they all point in one way. In the more globular tufts of the 

 weed the rolling motion is more irregular and the stem does not 

 always point in one direction, but the bunch may turn over, end for 

 end, occasionally; then the arrangement of the series of impressions 

 formed will often suddenly reverse right and left. In nearly all cases 

 where these impressions were seen they were observed under water 

 only, the weed drifting in from the channel off Dove Point, and 

 hence no photographs were obtained. Hitchcock's Ptilichnus 

 anomalus trails, as well as most of the impressions that he calls 

 Mnigmichnus multiformis, probably had some such origin as that 

 indicated above. 



A small branching twig of, say, a spruce or cedar would make a 

 trail like the Saltator impression which he describes, if it were rolling 

 over and over on the bottom under the influence of the advancing 

 or receding tide. A piece of a branch or a trunk, without notable 

 projections, being advanced along the bottom by rolling under the 

 influence of the rising tide, would make an impression like Hitchcock's 

 figure of sEnigmichnus multiformis given on Plate XIV of the "Sup- 

 plement to the Ichnology of New England." This slab was 3| feet 

 by 4| feet. The slab is crossed by "numerous rows of impressions, 

 certainly not less than thirty-five, the impressions are circular as 



