STRATIGRAPHIC AND GEOGRAPHIC DISTRIBUTION. 1 3 



Class Amphibia Linne, 1758 — Continued. 

 Subclass Lepospondylia Zittel, 1887. 

 Order Microsauria Dawson, 1863. 



Family AmphibaniidcB Cope, 1875. 



Amphibamus grandiceps Cope, 1865.' 

 Amphibamus thoracatus Moodie, 191 1. 

 Cephalerpeton ventriarmatum Moodie, 19 12. 

 Family Molgophidce Cope, 1875. 



Erpetobrachium mazonensis Moodie, 1912. 

 Subclass Stegocephala Cope, 1868. 



Order Temnospondylia Zittel, 1887. 

 Suborder Embolomeri Cope, 1885. 

 Family Cricotidw Cope, 1884. 



Spondylerpeton spinatum Moo6ie, igi 2. 



It will be seen from the above arrangement that nearly all of the orders of 

 Amphibia are represented in the Mazon Creek fauna. These animals are the oldest 

 known land vertebrates of North America. 



Contour interval SOfeet 



Fig. 3. — Portion of the "Morris sheet" of the U. S. Geological Survey, to show 

 topography and situations of the exposures of fossil-bearing shales at Mazon 

 River, a, the "Bartlett place," the so<alled "upper beds"; b, "lower beds." 



The writer was able, during July 191 1, to spend a week studying the fossil beds 

 (479) at Mazon Creek. The object of the visit was primarily to collect Amphibia, 

 but although several thousand nodules were examined, not one contained an 

 amphibian nor a fragment of one. Mr. J. C. Carr, of Morris, Illinois, who has collected 

 at Mazon Creek for more than 30 years, has never collected an amphibian. These 

 facts interested me in making the following comparison: If we take 100,000 nodules 

 as a basis for computation of the rarity of the various forms, something like the 

 following will be the approximate result of the investigation : 



