36 



Indiana University Studies 



ness from 25 to nearly 100 feet. It is a granular limestone in 

 which both the grains and cement are carbonate of lime. The 

 grains are made up, for the most part, of Foraminifera, Ostra- 

 coda, and bryozoan remains, mingled with fragments of other 

 forms, some of which have not been identified. The texture of 

 the stone varies in coarseness in different localities. The great 

 mass of the stone, however, is made up of the millions of 

 minute, in places almost microscopic, shells which are fairly 

 uniform in size; but in some localities the coarse stone is 

 abundant, as a result of the predominance of many larger 

 shells, such as gastropods and brachiopods. This latter variety 

 of stone is less valuable from the commercial point of view. 



The Salem limestone is quite massive, showing very few 

 bedding planes. Cross-bedded lamination is a frequent fea- 

 ture. The formation, in most places, carries two systems of 

 vertical joints, running approximately at right angles with 

 each other. The joints are rarely abundant, generally 20 to 40 

 feet apart. 



The variety in color of the Salem limestone proves to be a 

 feature of considerable importance in the investigation of the 

 origin of stylolites. The stone is of two shades of color, known 

 commercially as "buff" and ''blue". (The blue variety is more 

 of a gray, and in places is so light that it is almost white.) 

 The difference in the color of the stone is claimed to be the 

 result of a chemical change in the small amount of iron com- 

 pounds present, and an oxidation of the carbon content. Orig- 

 inally all of the stone was blue and the iron present was in the 

 form of ferrous compounds. The oxidation of the iron into 

 ferric compounds resulted in the original blue shade being 

 turned into a light brown, giving a buff color to the stone. 

 According to Hopkins (Hopkins and Siebenthal, 1897, p. 309 ; 

 1908, p. 314) 



The oxidation is a continuous process, not yet complete, carried on 

 mainly by the oxygen in solution in the meteoric water, the circulation 

 of which is accelerated or retarded by a variety of causes. 



The line of separation of the buff and blue stone is usually 

 very irregular. Consequently, there are blocks quarried in 

 which both colors are present." 



' For a full discussion of the cclor of the Salem limestone, reference should be made 

 to: Mance, G.C., 1917, p. 117; Hopkins, T.C. and Siebenthal, C.E., 1897, pp. 309-310; 

 1908, pp. 814-316. 



