STRATIGRAPHIC AND GEOGRAPHIC DISTRIBUTION. 15 



specimens of Pecopteris, are found quite definitely localized. These nodules are apt to 

 assume an irregular shape. These localizations of the fossils are, of course, what we 

 would expect from our knowledge of the recent fauna and flora. There is, to be sure, 

 more or less intermingling of the species. The myriapods, so far as they have been 

 found, are also localized. Mr. Carr found 3 within a space of a few feet, but again 

 these are found widely scattered. The exposures at the "upper beds" are about 

 a quarter of a mile long. They disappear under a heavy ledge of sandy limestone. 



At the "lower beds" (plate i, fig. 6), those further down the creek, conditions are 

 quite different from those just described, although of the same horizon; the banks 

 of the creek are higher and almost perpendicular, so that the chances of collection 

 from the shales are fewer. The bed of the creek, however, is wider and there are 

 more nodules washed out. The most abundant fossil at this place is Neuropteris. 

 The nodules at the upper end of the exposure are all, almost without exception, 

 barren of fossils. The exposures here are of about the same extent as the "upper 

 beds," though the species are not so varied. Judging from the collections made 

 while there, Arthropoda are more abundant at the "lower beds." 



Bradley (Geol. Surv. Illinois, iv, 196, 1870) mentions the occurrence of these 

 nodules at or near Morris. Other than these places the nodules have been thrown 

 out of a coal mine near Braid wood, Illinois. Doubtless close search would reveal 

 other localities where the shale is cut through in mining. The beds at both places 

 are slightly folded. This is true especially of the "upper beds," where a conspicuous 

 fold caused the beds to disappear in the bed of the creek and to reappear farther 

 down stream. This is directly across the large "ox-bow" bend of the creek. 



The beds at Mazon Creek were first explored in 1857 by Mr. Joseph Evans, 

 who sent his specimens to Berlin, Germany, where they excited great interest. It 

 was he who collected the type specimen of Amphibamus grandiceps Cope. Since 

 the time of Mr. Evans many have collected at Mazon Creek, and without doubt 

 the fossil-bearing nodules from this locality are more widely scattered in the 

 museums of the world than are organic remains from any other one horizon. 



So far as we know there was no upland vertebrate life at that time. The forms 

 at present known were confined to the water or the margins of the water. The 

 absence of knowledge of upland and terrestrial deposits of this time doubtless 

 accounts for the absence of known vertebrates. It is, however, especially interesting 

 to speculate on the ancestral types of the land vertebrates, and it must be admitted 

 that the Coal Measures Amphibia as at present known throw the ancestry of land- 

 living vertebrates far back into geological time. 



(m) The Cannelton slates of Beaver County, Pennsylvania, have furnished 3 

 species of Amphibia and fragments of other species are represented in the U. S. 

 National Museum (462). The species so far known are: Tuditanus minimus 

 Moodie, Erpetosaurus sculptMs Moodie, Erpetosaurus minutus Moodie. 



They are the first evidence of the -occurrence of amphibian remains in these 

 deposits. The Cannelton specimens are found in a thin stratum of slate which forms 

 part of the Middle Cannelton Coal. The Cannelton slate, in which the fossils occur, 

 forms the roof of the Middle Kittanning Coal, which is only 20 to 30 feet above the 



