188 A POPULAR EXPOSITION OF THE 
however, led to the inference that they were really made by a much 
lower animal, an extinct crustacean, probably more or less akin to the 
modern Jimulus. The generic name of Protichnites has been be- 
stowed on these tracks by Professor Owen. They present several 
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Fig. 156.—Protichnites alternans (Owen). Fig. 157—Climactichnites Wilsoni (Logan). 
varieties, but exhibit essentially a narrow and often interrupted 
central groove with a parallel series of pit-marks on each side, as 
shewn in fig. 156. The groove is supposed to have been made by 
the caudal shield or tail-spine of the animal, and the pit-marks by 
the creature’s claws. Tracks of Protichnites occur at other locali- 
ties in Beauharnois, and likewise in Vaudreuil, &c., in Eastern Canada. 
They have also been found near the Town of Perth in the Township 
of Drummond, Canada West, where they are accompanied by the 
second kind of track impressions alluded to above. These latter 
exhibit narrow bands about five or six inches in width, with 
“beaded” edges, and usually a central beaded line crossed by a 
transverse series of curved or straight ridges: the whole presenting, 
as stated by Sir William Logan, a general resemblance to a rope- 
ladder. An idea of this appearance may be gleaned from fig. 157. 
On account of their ladder-like aspect, Sir William Logan has desig- 
nated these tracks under the generic name of Climactichnites. Fig. 
157 represents C. Wilsoni (Logan), so named from the discoverer 
of there latter impressions, Dr. Wilson of Perth, to whose explora- 
tions Canadian geology is also largely indebted in various other 
respects. 
The more important economic materials of the Potsdam Group 
comprise building stones of good quality, as those from Lyn and 
Nepean employed in the construction of the Parliament Buildings 
at Ottawa; sandstones for glass-making purposes, being almost free 
from oxide of iron (Beauharnois, Vaudreuil),; and sands and sand- 
stones for lining the sides and floors of iron furnaces. The friable 
sandstone of the Township of Pittsburg (just east of Kingston), 
and other beds on the St. Maurice in Eastern Canada, are largely 
