Xo. 4!)!)] 



DWARF FAUNAS 



4M 



break. That some at least of these beds were deposited 

 in shallow water and even exposed at times to the sun is 

 shown by the presence of cross bedding, ripple marks, 

 and mud cracks. As is usually the ease, these faunas 

 show more strongly their dwarfed condition when viewed 

 as a whole than when distinct individuals are considered; 

 for the reduction in size has not been very great in indi- 

 vidual eases, but is shown slightly in nearly all of the 

 forms. For example, Whitfirhlella nueh'olata is equally 

 small in all three of the formations (Cobleskill, Rondout 

 and Manlius) ; the Spirifers, likewise, are conspicuous for 

 their small size, 8. corallinotsis and S. cn'oisis from the 

 two lower horizons and S. vanuxemi from the Manlius. 

 Favosites precedent is a small form of F. helderbergice 

 found in the two lower horizons. The presence of a lime 

 mud seems to indicate that the waters in which deposition 

 took place was denser with alkalies than normal sea water, 

 otherwise the mud would have gone into solution as is 

 usually the case when limestone is eroded. Such abnormal 

 conditions would have a dwarfing effect upon the indi- 

 viduals living there, as has been noted in the case of the 

 Mediterranean. To this unfavorable influence would be 

 added the mechanical impurities of the mud, for on ac- 

 count of the shallowness of the water, the mud would 

 probably be kept by the waves in an almost constant state 

 of suspension. The occurrence of these dwarf faunas be- 

 tween the periods of small exceedingly dense seas or 

 lakes, depositing salt and gypsum, and the normal marine 

 conditions of the Helderbergian is an additional proof of 

 the greater-than-normal density of the water at that time. 



b. An exceedingly interesting dwarf fauna is that of the 

 Pvrite laver in western New York at the horizon of the 

 Tully limestone, but where that stratum is otherwise miss- 

 ing. This fauna is very fully discussed by Professor F. 

 B. Loomis. 23 



The layer is a more or less discontinuous deposit of 

 pyrite appearing as very broad lenses but not over 1 foot 

 in thickness. It contains a fauna of not less than 45 



