GVrSUM DEPOSITS OF NEW YORK 69 



Mode of origin applicable to the New York deposits 



There is no doubt that the gypsum of the Salina beds has been 

 deposited by evaporation of surface waters and is an integral part 

 of the stratified succession. This view is advocated or tacitly im- 

 plied in most descriptions of the New York deposits that have 

 already been published, though it has not escaped criticism. The 

 evidences which form the application of this method to the ex- 

 clusion of other theories may be summarized under the following 

 heads : 



1 Form and structure of deposits 



2 Associations of the g>'psum 



3 Biologic conditions in Salina time 



1 The occurrence of the gypsum in thin lenses which are of the 

 same degree of continuity as the inclosing strata indicates an ac- 

 cumulation concordant w4th the salt, shales and limestone of the 

 Salina. The lenses, in most instances at least, thin out very grad- 

 ually, showing only moderate changes of thickness as they are 

 traced from place to place and few irregularities not common to 

 sediments ir^ general. If the gypsum were formed by the reaction 

 of acid waters upon limestone, variations in form like those found 

 in replacement dej^osits of metallic minerals would be expected. 

 The type of deposits in which the g}'psum occurs as nodular masses 

 with a thickness nearly equal to the horizontal dimensions — as fig- 

 ured by Hall and represented in Dana's Manual — is certainly the 

 exception and not the rule and is the result probably of solution 

 of the larger masses by underground waters. Such deposits are 

 illustrated in figures 3 and 4 on page 25. 



The undisturbed condition of the beds as generally observed is 

 also against any theory of secondary deposition either by reaction 

 upon limestone or by precipitation from ground waters. The change 

 from limestone to gypsum involves an increase of 90 per cent in 

 the volume, which would hardly occur without general disturbance 

 of the adjacent strata. The beds, also, are not faulted or fractured 

 so as to permit the easy circulation of waters in vertical direction. 



2 The close relation of the gypsum to the salt deposits is such as 

 would be expected from the evaporation of sea water. While the 

 fact that the salt underlies the main gypsum beds, whereas the re- 

 verse is the natural order, seems to controvert this view, an ex- 

 planation for it may be found without recourse to extraordinary 

 conditions of evaporation and supply of the sea waters. If the 



