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NEW YORK STATE MUSEUM 



others which might be cited, an unfavorable medium has caused 

 dwarfing among the animals inhabiting it, and in the above 

 instances the media have been modified by an unusual chemical 



change. 



Such was also the case in the sea in which the Tully pyrite was 

 formed. It was a shallow water area, perhaps landlocked in a 

 measure and undoubtedly running shoreward into low coastal 

 marshes. Its waters were surcharged with iron in solution, 

 probably a ferrous carbonate; and over its bottom was a pro- 

 fusion of decaying organic matter. Such decaying matter would 

 give off sulfuretted hydrogen. 1 We have here two chemical 

 agents at work, either separately or in combination, either of 

 which would be an unfavorable element in the environment. 

 There is very little if any distortion among these species. The 

 dwarf condition may be attributed either to the presence of the 

 iron, to the gases escaping from decomposition or to both. The 

 pyrite is an insoluble compound and represents the precipitate 

 formed by the iron and the gases of decomposition. The dwarf 

 condition is coextensive with the deposit of iron. It is perhaps 

 not surprising that these forms should be dwarf, but that 

 they could live and retain their characters enough to make them 

 recognizable while attaining only one fifteenth their normal size, 

 is noteworthy. 



The reaction which would deposit pyrite in such a sea is 

 familiar. The iron, as ferrous carbonate, would unite with the sul- 

 furetted hydrogen to form pyrite, carbonic dioxide gas and water 

 (FeCO s +2(H 2 S) +0=FeS 2 +C0 2 +2 (H 2 0) . There are probably 

 more steps in the process than the formula indicates, but the end 

 results would be as stated. In the pyrite, as it has formed by 

 precipitation, the fossils have been ingulfed, having died on the 

 spot where they are found. This is evident from the fact that the 

 bivalves when preserved, have both valves intact, which would 

 not be so likely to occur if the shallow sea had been exposed to 

 the play of the waves. The iron-carrying waters were not 

 entirely disconnected from the purer waters of the sea without, 

 for into these pyrite faunas come occasional representatives of 



1 Dr Dall tells me that occasionally after heavy rains HuS is carried out into 

 the waters along the coast of Florida, and that many animals are killed thereby, 

 and'others, which withstand the influence better, are distorted. . 



