{Continued from preceding page) 

 of the brown ground-mass of the pellet, 

 separated from the pellet by a band of 

 shale 2 millimeters thick. Our inter- 

 pretation of this interesting picture is as 

 follows : the shark regurgitated the stom- 

 ach residue mass, which settled to the 

 bottom. There it decayed in the pres- 

 ence of air dissolved in the water. Gas 

 bubbles formed and escaped, and the 

 process of decay reduced the volume of 

 the pellet in its upper half, hence the 

 flattened upper side. Then one final 

 bubble formed in the middle of the pel- 

 let. As it grew bigger, the palaeoniscoid 

 scales in its vicinity became tangentially 

 aligned to its surface. Then the bubble 

 escaped; as it left the residue mass, it 

 drew a palaeoniscoid scale up into the 

 escape channel, along with a bit of 

 ground-mass. The scale was held in 

 vertical position by the mud that had 

 meantime accumulated on the pellet. 

 The bit of ground-mass settled on the 

 mud surface. Hence, the distance be- 

 tween the little "flag" of ground-mass 

 and the surface of the pellet is the thick- 

 ness of shale that had accumulated on 

 the pellet during its phase of decay. 

 This distance was 2 millimeters. Simi- 

 lar measurements on other specimens 

 from the Logan Quarry were the same; 

 in specimens from the Mecca Quarry, 

 the comparable measurement was con- 

 sistently 1 millimeter. 2 



In order to learn how long it actually 

 took to deposit this measured thickness 

 of shale — and so "tell the time" by our 

 clock — we now need a reasonable esti- 

 mate of how long it took a fish to decay 

 to bare bones at the site of the ancient 

 fish traps of Mecca. 



We are probably safe in assuming that 

 bacterial decomposition of animal tis- 

 sues in the presence of air was much the 



2 The curious aspect of this phenomenon is 

 that the thickness of shale so measured appears 

 also to have been the thickness of mud at the 

 time of deposition. Ordinarily, as mud be- 

 comes compacted into shale, one would expect 

 a severe reduction in volume. In this case, 

 however, a great deal of additional evidence 

 suggests that the Mecca and Logan Quarry 

 shales did not undergo compaction in the gen- 

 erally accepted sense, but that compaction took 

 place largely at the time of deposition. 



Fig. 1. Two photographs of a section cut through a stomach 

 residue pellet of a shark from the Logan Quarry. 



same process in Pennsylvanian time as it 

 is today. The rate of decay today varies 

 greatly with the temperature and there 

 is good reason to believe that this was 

 also true in the geologic past. 



The question as to the climate of Penn- 

 sylvanian time has been much discussed, 

 especially in connection with the origin 

 of the coal beds that characterize rock 

 sequences of this period all over the 

 world. The evidence is primarily of a 

 paleobotanical nature and is by no 

 means wholly conclusive. But most pa- 

 leobotanists agree that the Pennsylva- 

 nian climate must have been rather 

 warm and devoid of sharp, seasonal tem- 

 perature differences. 



For these reasons we chose the bayou 

 country of Louisiana to determine, by 



field experiment, the rate of bacterial 

 decay of fishes under conditions that 

 were probably quite similar to those of 

 the ancient Mecca fish traps. At tem- 

 peratures between 20° and 30° C, fishes 

 weighing three-fourths of a pound de- 

 composed to the bare skeleton in less 

 than one week. It would thus seem rea- 

 sonable to assume a similar rate of decay 

 for the fishes now enclosed in the Mecca 

 and Logan Quarry shales. 



As described above, it was possible to 

 measure the amount of shale (1 milli- 

 meter in the case of the Mecca Quarry 

 shale) that had accumulated above a 

 carcass during its process of decay. Since 

 we may assume that the decay process 

 at the ancient burial site near Mecca 

 {Continued on page 8) 



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