Fossil Tracks from the Potsdam Sandstone. 



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which, moreover, are not usually straight and exactly transverse, 

 but most frequently Y-shaped with the apex of the V pointing 

 forward. This form, though the prevailing one, is nevertheless 

 subject to the following modifications : The angle varies in the 



Plate 1- 



-Fossil Tracks on Potsdam Sandstone. 

 .(From photograph.) 



typical cases from the extreme limit of 110° to 185°. When the 

 Y becomes distorted, this angle appears to vary further, through 

 larger angles, till, in various cases, it disappears, and the ridges 

 are straight. This occurs somewhat more commonly in the 

 smaller tracks. 



Another frequent variation is in the relative length of the arms 

 of the Y, and the consequent shifting of the point towards one 



