26 PROCEEDINGS OF THE CHICAGO MEETING 



At 12.30 o'clock the Society adjourned for luncheon, reconvening at 

 3.15 p. m. in two sections for the reading of papers. Under the chair- 

 manship of Vice-President George P. Merrill the following papers were 

 presented : 



TITLES AND ABSTRACTS OF PAPERS PRESENTED BEFORE THE AFTERNOON 

 SESSION AND DISCUSSIONS THEREON 



8YNGENETIC ORIGIN OF CONCRETIONS IN SHALE 

 BY W. A. TABR 



(Abstract) 



Studies of calcareous and siliceous concretions occurring in shale in the 

 Cretaceous in South Dakota, Wyoming, Montana, and in the Pennsylvanian in 

 Missouri have led to the conclusion that these concretions were formed con- 

 temporaneously with the inclosing beds. The evidence supporting this view is 

 as follows : the concretions lying along one bedding plane, the recurrence of 

 bands of concretions at fairly regular intervals, the relationship of the con- 

 cretions to the bedding planes, and certain features of the concretions them- 

 selves. 



Discussion 



Dr. Stephen Tabeu: A few years ago I studied some calcareous concretions 

 in shales near Union Springs, Cayuga County, New York. I was struck by 

 the sympathy shown by many of the concretions with respect to a plane bisect- 

 ing them parallel to the bedding. Where this sympathy is shown by concre- 

 tions I think that it indicates their growth subsequent to the deposition of the 

 overlying beds, for absence of material on top would make growth easier in 

 that direction and subsequently result in unsymmetrical concretions. 



Prof. G. H. Chadwick : Concretions in the upper Devonian Portage shales 

 of western New York are arranged in definite planes, as described by Professor 

 Tarr, but among these are large ones, as figured long ago by James Hall in 

 his report on the Geology of the Fourth District of New York, with cone-in- 

 cone structures constituting the upper and under sides of the concretions. 

 These suggest that the concretions have grown subsequently and exerted 

 pressure against the inclosed strata. 



Dr. Sidney Powers : Concretions of impure limestone at the Butler salt 

 dome, in Texas, described in the American Journal of Science, 1920, show re- 

 placement by iron carbonate which has caused the development of cone-in-cone 

 structure. This structure distorts and destroys the fossils in the concretions. 

 The concretions were evidently formed contemporaneously with sedimentation. 



Prof. R. D. Salisbury : Certain calcareous concretions in shale about which 

 laminae bend appear to be syngenetic. These concretions appear to have grown 

 in a shale and to have bent laminse up above themselves and down beneath. 

 In these cases laminae are greatly thinned above the highest part of the con- 

 cretions and below the lowest, while at the sides of the concretion between the 



