minerals that they contain, thus reflecting periods of high water 

 (gray shales, with a great amount of clay minerals) and periods of low 

 water (black shales containing relatively small amounts of clay). 

 The results obtained so far indicate periodic changes between stages 

 of high and low water. 



The study has employed the results of the examination of the 

 speed of bacterial decomposition of fishes under a variety of natural 

 situations in Louisiana (see Annual Report 1956, pages 52-53) sim- 

 ilar to those that produced the Mecca shales. As a factor for deter- 

 mining the time involved in the deposition of the shales, it was found 

 that each high and low water cycle lies within a period of the order 

 of magnitude of one year, showing that four years were required for 

 deposition of the entire shale profile of 12 inches. These results, 

 although highly significant, are only part of the many-faceted Mecca 

 problem. The specific character of the environment at the site of 

 the Mecca quarry, the regional picture in the vicinity of Mecca, and 

 the setting of the Mecca area within the overall geographic distribu- 

 tion of land, coal swamp, and marsh and the open inland sea of the 

 time, as well as the detailed reconstruction of events that followed 

 the initial inundation of the Mecca area by the sea, require the analy- 

 sis of the entire fossil collection from the Mecca quarry, as well as 

 from many localities in the area, and stratigraphic findings in Parke 

 and Vermillion counties, Indiana (see page 34). 



In the course of such field work early in the spring Curators Zan- 

 gerl and Richardson discovered, in a gully some 15 miles north of the 

 Mecca quarry site, a piece of shale that was covered entirely with the 

 undisturbed shagreen (placoid scales) of the skin of a very large 

 shark. This discovery led to the excavation of what may safely be 

 called the most perfectly preserved shark ever found in the Pennsyl- 

 vanian the world over and to the opening up of a second quarry far 

 larger than the one at Mecca. The excavation is located on the land 

 of Mr. and Mrs. P. Herbert Logan of Indianapolis, Indiana, whose 

 kind permission to open a quarry is gratefully acknowledged. Chief 

 Preparator Gilpin and Preparator Erickson assisted in the initial exca- 

 vation of the large shark. Miss Barbara Best and Miss L. Margot 

 Marples, Antioch College students, worked in the laboratory on 

 preparation of the quarried material. 



Curator Zangerl, with Dr. Frederick J. Medem of Colombia, Field 

 Associate in the Department of Zoology of the Museum, described a 

 new side-neck turtle of the subgenus Batrachemys (genus Phrynops) . 

 In connection with this study Curator Zangerl was invited by Dr. 

 Ernest Williams, Curator of Reptiles and Amphibians at the Museum 

 of Comparative Zoology at Harvard University, to spend a week at 



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