FOOTPRINTS IN THE ROCKS. 437 



surprise, for it is commonly supposed that these animals never leave 

 the water for the land. It has been ascertained by naturalists that 

 certain varieties of tropical fish often leave the water, and walk, or 

 rather hobble, on the shore, using their fins for legs. This they can do 

 for days together. They have also been known to climb trees in 

 search of sustenance. Their track-way would be peculiar, consisting 

 of two rows of dots or round impressions, made by the prominent 

 sharp spine of the fin, accompanied by various trails produced by the 

 shorter rays, body, and tail. One species of the Ichnozoa has made 

 a trail so much like the markings of these tropical fish that we must 

 believe the Siluridce had other representatives in the Triassic waters. 

 Another impression seems to have been made by an ordinary fish 

 striking his fins against the ridges between ripple-marks in very shal- 

 low water. 



With considerable hesitation, thirty-four species of Ichnozoa may 

 be referred to insects. These animals generally have six feet. If at- 

 tention be paid to the manner in which the common fly walks, it will 

 appear that every foot is brought to the ground, each in a different 

 place, so that every extremity makes a mark. A fly that has been 

 immersed in a colored fluid, and then travels over a sheet of white 

 paper, will leave impressions as distinct as those found upon stone, 

 and the colored track-ways must be our guides to the affinities of the 

 ancient ichnites, like the Copeza. 



Fia. 5. 



Copeza. 



Between these ancient and modern impressions it is difficult to find 

 marked differences, except of size. Each displays two rows of im- 

 pressions in groups of three, the several clusters alternating with one 

 another. Of the three marks or lines in each cluster, the inner is al- 

 most at right angles with the line of march, the central and outer 

 point backward, the latter the most. 



We may suppose that each group of markings was made by the 

 three feet on each side of the animal, the inner impressions by the 



