PALEOZOIC TIME — CARBONIC. 



645 



eight inches. There is also a distinct impression of a tail, an inch or more 

 wide. The slab is crossed by a few distinct ripple-marks (eight or nine 

 inches apart), which are partially obliterated by the tread. The whole sur- 

 face, including the footprints, is covered throughout with rain-drop 

 impressions. 



1028. 



Tracks of Sauropus primaevus (x J). I. Lea. 



We thus learn that in the region about Pottsville a mud-flat was left by 

 the retreating waters, perhaps those of an ebbing tide, covered with ripple- 

 marks ; that the ripples were still fresh when a large Amphibian crossed 

 the flat ; that a brief shower of rain followed, dotting with its drops the 

 half-dried mud ; that the waters again flowed over the flat, making new de- 

 posits of detritus, and so buried the records. The records were opened and 

 deciphered in 1849 by Dr. Lea. 



Characteristic Species. 



Plants. — In the Subcarboniferous of Pennsylvania occur, according to Lesquereux, 

 Archceopteris obtusa Lx., and A. minor Lx. (both found in the Chemung of the Devonian) , 

 A. Bockschiana Gopp. ; remains of Lepidodendron, as L. corrugatum Dn., and Stigmaria 

 minuta Lx. ; in Illinois, in the Chester group, the Ferns Megaphyton protuherans Lx., 

 Caulopteris Wortheni Lx. , Alethopteris Hele7ice Lx., JSfeuropteris capitata Lx., Pseudope- 

 copteris anceps Lx., Rhacopliyllum flabellatum St., Sphenopteris cristata St., Megalopteris 

 fascicidata Lx. ; also Lepidodendron costahtm Lx. , L. turhinatum Lx., L. obscurum Lx., 

 L. Veltheimanum St., L. Wo7-theni 'Lx. , Stigmaria anabathra Corda, S. mmor Gopp., S. 

 umbonata Lx., Knorria imbricata St., Calamites Suckovi Bngt., Asterophyllites equiseti- 

 formis Schl., and others. 



In the Chester group of Indiana, according to CoUett, occur Stigmaria, Lepidodendron 

 aculeatum St., L. diplostegioides Lx. , L. foriilatum Lx., Lepidostrobus, Knorria, Neurop- 

 teris biformis, AlethopAeris , etc. One specimen of Lepidodendron had portions of the 

 leaves attached to the stem, which were 12 to 14 inches long, though only from one eighth 

 to one fourth of an inch in width. 



In the Subcarboniferous of Nova Scotia and New Brunswick, Dawson has made out 

 the following species: Ferns — Cyclopteris Acadica Dn. , Cardiopteris, Hymenophyllites ; 

 Lycopods — Ptilophyton plumula Dn., the last of the genus, Lepidodendron corrugatiim 

 Dn. (near L. Veltheimanum of Europe), L. tetragonum St., L. obovatnm St., L. dichoto- 



