No. 499] 



DWARF FAUX AS 



483 



The same species of gastropods and cephalopods vary 

 considerably in size, much more so than do the brachio- 

 pods. 



Since "iron solution in water tends to settle gradually 

 to the bottom, as was found in experimenting on the fishes 

 ... it is not surprising to find that the brachiopods, 

 which are either sessile or lie on the bottom, are the most 

 dwarfed." 27 The brachiopods are seldom one fifteenth 

 the normal in size, nor do they vary much from this ; while 

 the gastropods and cephalopods, groups of greater 

 freedom of motion often vary in the same species from 

 one twenty-fifth to one half the normal size ; those which 

 evidently grew up in this iron water being much smaller 

 than those which entered it when partly grown. "All of 

 these fossils then represent cases of arrested develop- 

 ment, with the understanding that the arrest is at no given 

 point but all through the development." 28 It is thus a 

 case rather of retarded development or bradygenesis. 



These retarded individuals appear like the young of 

 earlier Devonian types. 



c. From analogy with the Black Sea deposit, Clarke 20 

 conceives that the black, very thinly and evenly laminated 

 shales of the Genesee in western New York, with their 

 dwarf invertebrate fauna and fish, with their abundant 

 segregation of iron sulfide, limestone nodules, etc., are 

 likewise the result of accumulation in waters of great 

 depth and imperfect vertical circulation. Dr. Clarke 

 notes the presence of surface ocean currents in this 

 region. He thus interprets the Styliolina limestone, four 

 to six inches thick, at the base of the Genesee in western 

 New York, as essentially a pteropod ooze caused by the 

 meeting of a cold northern current and a warm southern 

 one bearing these pteropods. The cold current thus acted 

 as a barrier to the northwest spread of these pteropods. 



An accessory agent in the production of this dwarf 



