[486] 



ON THE PROBABLE NATURE OF THE SUPPOSED 

 FOSSIL TRACKS 



KNOWN AS PROTICHNITES AND CLIMACTICHNITES. 



BY E. J. CHAPMAN, Ph.D., 



Professor of Mineralogy and Geology in University College, Toronto. 



The Potsdam sandstone of Beauharnois and Yaudreuil (near the, 

 junction of the St. Lawrence and Ottawa rivers), and the same 

 formation in the vicinity of Perth in Eastern Ontario, is well known 

 to exhibit in places some remarkable track-like impressions, commonly 

 known as " Protichnites tracks." These were at first supposed by 

 Professor Owen to have been made by a tortoise, but were after- 

 wards regarded as the tracks of several species of some unknown 

 crustacean, " wholly distinct from anything presented by the crusta- 

 cean foi-ms of later geological periods or of the present day." They 

 may be described generally as presenting in some cases a continuous 

 — and in others an interrupted — central furrow, with a series of small 

 pit-marks or indentations, at a distance of two or three inches on each 

 side, along the entire length of the impression. The central furrow, 

 or line of broken furrows, is regarded, by those who assume these 

 impressions to be of animal origin, as having been formed by a ridge 

 on the plastron of the crustacean, or perhaps by a styliform appendage 

 attached, as in the limulus, to the abdomen of the animal, whilst the 

 creature propelled itself by its numei'ous feet in shallow depths of 

 water, or dragged itself along the exposed sea shore. In at least one 

 of the discovered impressions, however, the lateral indentations are 

 absent, and the impression consists simply of a strongly-marked cen- 

 tral furrow, with a few parallel grooves on each side, the outermost 

 of these being at a distance of a couple of inches or thereabouts from 

 the median furrow. The absence of lateral pit-marks in this case, 

 and the occurrence in their place of narrow grooves, was occasioned, 

 it has been suggested, "by the limbs of the animal having been 

 di-agged along while the body was afloat." The impressions are 



