SIXTH REPORT OF THE DIRECTOR igOQ 33. 



west to Erie. The gypsum deposits are found in the upper part 

 of the Salina formation which outcrops as far east as Albany 

 county, but they attain workable dimensions only in the central 

 and western areas where the Salina beds are thickest. Within 

 this section which measures over 150 miles east and west they 

 show a wide range of character, as one might expect; while there 

 is also considerable variation in the size and sequence of the 

 bodies. 



Chemical analysis of various selected rock samples indicates 

 that a relation more or less consistent exists between the com- 

 position and geographic distribution of the gypsum. In general 

 it may be said that there is a progressive increase in the per- 

 centages of gypsum substance and a corresponding improve- 

 ment in physical qualities as the deposits are traced to the west. 

 This relation may be the expression of original conditions sur- 

 rounding their accumulation which will later be considered. In 

 the eastern counties the gypsum is admixed with clay, lime and 

 magnesian carbonates and silica, the proportion of these impuri- 

 ties ranging up to 25 per cent or more of the whole mass. On 

 the other hand the deposits in the western part of the belt show 

 as little as 5 per cent of foreign ingredients and are much lighter 

 in color. 



The valuable bodies occur interbedded in the Upper Salina 

 shales. They occupy usually large areas, as compared with 

 their vertical dimensions, or in other words are stratiform. 

 There are, of course, variations and irregularities to be found, 

 but the stratiform type is the predominant and original one ; 

 the extreme departures from that type such as have been de- 

 scribed and figured in the reports of James Hall and in Dana's 

 Manual are in most instances to be regarded as modifications 

 brought about by the solvent eitects of ground waters. Besides 

 the larger beds small seams of crystallized transparent gypsum, 

 which appear to be secondary depositions, occur through the 

 shales, so abundantly distributed in some places that the mixed 

 shale and gypsum has been worked during times past to supply 

 local needs for land plaster. 



The forthcoming report will include a consideration of the 

 origin of the gypsum, a subject that has economic bearings as 

 well as geologic interest. Without entering into details of evi- 

 dence here, it may be said that the gypsum is considered an 

 accumulation from sea water evaporation contemporaneous in 



