1877. ] Concerning Foot-Prints. 415 
pression to some unknown crustacean of a higher degree of organ- 
ization than ariy of the animals we have enumerated, which was 
literally the king-crab along the shores where it made its home. 
The Potsdam sandstone has also yielded another series of 
foot-prints fully as large as Protichnites, called Climactichnites, 
in reference to their striking resemblance to a rope-ladder. These 
impressions (Figure 78) consist of two furrows, about six inches 
apart, the interspace crossed by parallel curved furrows that rep- 
resent the rounds of the rope-ladder ; there are also indications of 
a medial furrow, as in Protichnites. Of the animal that formed 
these trails even less is known, as can be inferred, than of those 
whose tracks we have been considering. They are supposed by 
some persons to be the track left by a huge trilobite, like Para- 
doxides Harlani; others consider them as the trail of a large 
gasteropod, no other records of which“are known. Although the 
trail known as Climactichnites differs greatly in appearance from 
Protichnites, yet it is not impossible that they were formed by 
the same animal under different conditions: one impressed upon 
the sands while walking, the other, perhaps, formed by the swim- 
ming appendages, which are supposed to have resembled those 
of the Limulus. 
As we have seen, the crustaceans were the highest forms of 
life in the Silurian oceans ; their reign was terminated, however, 
about the close of the upper Silurian, by the introduction of 
fishes, which continued to be the rulers of the ocean throughout 
the Devonian age, which, for this reason, is often spoken of as 
the age of fishes. Another great advance was made in the life of 
the globe during the Carboniferous age, when the air-breathing 
reptiles first came upon the stage of being. The existence of 
these more highly organized animals in the Carboniferous age 
was first made known by the discovery of their foot-prints. The 
honor of first bringing these interesting relics to the notice of 
geologists is due also to Sir William Logan, who discovered rep- 
tilian foot-prints on slabs of Carboniferous sandstone in 1841, at 
Horton Bluff, Nova Scotia. Shortly afterwards, the well-known 
discovery of the foot-prints of a large amphibian, named Sauropus 
Primevus, was made at Pottsville, Pa. For some time the foot 
prints of these ancient reptiles were the only evidence known of 
their existence. These scanty records, however, were enough to 
demonstrate that lizard-like reptiles, of considerable size and of a 
high organization, existed during the age in which the coal de- 
posits of Nova Scotia and Pennsylvania were formed. 
