384 W. A. TARR SYNGENETIC ORIGIN OF CONCRETIONS IN SHALE 



(7) The occurrence of concretions dominantly along one bedding 

 plane should be accepted as indicating a syngenetic origin for such con- 

 cretions as readily as we accept a syngenetic origin for beds of limestone 

 under similar conditions. 



(8) The perfect preservation of fossils within the concretions points 

 to its development previous to burial. 



(9) It is difficult to understand how an insoluble material like silica 

 can be aggregated in an impermeable material like shales, or how and 

 why the large amount of calcareous material in the successive lines of 

 concretions, as in the Carlisle formation, should be concentrated along 

 these planes, unless we accept a syngenetic origin for at least a part of 

 the concretions in shales. 



