234 



C. H. White — Autophytography . 



during decay. For the precipitate to remain permanent, 

 ammonia must be produced gradually and in sufficient quantity 

 to neutralize the acid in the iron-bearing solution until the 

 acid ceases to flow to the point of deposition. That vege- 

 table matter undergoing decay will under certain and usual 

 conditions produce acids which take iron in solution, and 

 will under other conditions yield ammonia, is well known 

 and need not be discussed here ; but the nicety of adjust- 

 ment of these conditions called for above would necessarily 

 be rare, and, — if this be the correct theory, — would account 

 for the scarcity of autophytographs of this description. 



In figures 3, 4 and 5 are reproduced autophytographs of the 

 negative type. The specimens represented by figures 3 and 4 

 are autophytographs of recent formation that were collected 

 by Professor J. B. Wood worth of Harvard University, and it 

 is through his kindness that they are here reproduced. The 

 specimen represented by figure 3 is a block of sandstone, taken 

 from the Saratogan, or upper Cambrian, formation near Bid- 

 die's Crossing, about a mile and three-quarters north of Sciota, 

 Moore's quadrangle, Clinton County, New York, on which 

 rootlets have in recent time brought about solution of the iron- 

 pigment which stained the sandstone a yellow-brown, giving 

 an autophytograph of lighter color on a dark background. 

 Figure 4 represents a specimen taken from the ploughed sur- 

 face of a lateral moraine at the west base of Bald Hill near 

 Caroline Depot, Tompkins County, New York. This specimen 



