FOOTPRINTS IN THE ROCKS. 439 



As might be expected, there was a group of Crustaceans, animals 

 who frequent the mud left at low tide. Their impressions have been 

 left on the rocks from the dawn of the Paleozoic age to the very latest 

 period. The famous Prototichnites of Canada upon the Potsdam sand- 

 stone, so ably described by Logan and Owen, are generally thought 

 to have been made by gigantic representatives of this class, though 

 hardly by the Pterogotus form, as suggested by Salter and Woodward, 

 because the latter were exclusively swimming animals. The Prototich- 

 nites were not represented in the Trias. The forms preserved at Am- 

 herst are peculiar, and not to be referred to any special order of 

 Crustacea. One was a giant with a track-way 27 yards wide, and the 

 idea suggested by its inspection is that of an animal with small body 

 stilted high upon very long legs. 



Other species of Ichnozoa may have been Annelids, Avith their 

 sinuous, fimbriated line of march, toorms, mollusTcs, with single, double, 

 or treble depressed lines, and various larval forms whether like those 

 crawling over the surface or making burrows in the mud. A square 

 rod of this Triassic surface will be as thoroughly carved by these 

 various impressions, produced by the lower orders of animal life, as 

 the same surface of the sea-shore in temperate or tropical climes at 

 the present day. 



Thus this brief review of the different classes of Triassic Ichnozoa 

 shows a natural assemblage, such as might be found associated in 

 maritime districts. The huge birds associated with kangaroodike 

 forms reminds us immediately of the modern Australian realm, with 

 the cassowaries and the long list of marsupials. Indeed, it would not 

 be strange if the assemblage of life which first showed itself in the 

 American Triassic estuaries had gradually migrated eastward over re- 

 gions now covered by the Northern Atlantic, pushing farther and far- 

 ther in each g-eoloscical era till the ultima Thule of Australia is reached, 

 where the modern representatives of the Ichnozoa were prevented from 

 further migration by the termination of continental areas. Soon after 

 its occupation, Australia must have been separated from the Asiatic 

 Continent by a partial submergence, so that the peculiar fauna became 

 restricted, and none of the animals could retrace their steps toward 

 the setting sun, even if they desired. It may be, then, that historic 

 Australia represents Triassic New England in its faunal peculiarities 

 terrestrial, but not maritime, since marine animals cannot so easily be 

 restricted in their migrations or developments. 



Besides footprints, other markings on the Connecticut sandstone 

 attract our attention. We observe the marks of rain-drops, ripples of 

 the waves, shrinkage-cracks, broken bubbles arising from marsh-gas, 

 septaria, rarely a shell, a possible echinoderra, coprolites of birds as 

 determined by chemical analysis, a few reptilian bones, bark and cones 

 of gymnosperms, besides other curious marine and terrestrial plants, 

 remain. 



