74 proceedings of the chicago meeting 



Session of Thursday Afternoon, December 30 



The afternoon session began at 2.07 o'clock, with President I. C. White 

 in the chair. The discussion of Doctor Thiessen's paper was continued. 



Discussion of Doctor Thiessen's paper continued 



Prof. Frank R. Van Horn : I would like to point out to Doctor Tlieissen 

 that a probable reason for the Marcellus shale differing in structure from the 

 Devonian sliales of Illinois, Tennessee, and others of later age from Colorado 

 and Utah is that the Marcellus, in my experience, is more highly calcareous. 

 It is filled witli brachiopod remains. Correspondingly, it is less dense and 

 therefore more porous and allows later structures to form in three directions 

 across the bedding and is not limited to two directions in more dense argilla- 

 ceous shales. 



The constant presence of pyrite in all these sections may throw considerable 

 light on the formation of concretions and possibly on their origin. In a previ- 

 ous paper Dr. W. A. Tarr argues for tlie syngenetic origin of concretions. 

 Some of the shales in this paper certainly show that these pyrite cubes and 

 concentric concretions were formed later than the stratification planes. I wish 

 also to suggest that these pyrite concretions may have been formed by the 

 reduction of ferrous sulfate solutions by the large amount of vegetable matter 

 in these oil and other shales. All are familiar with the ironstone concretions 

 from Mazon Creek, Illinois, with the fossil forms at their" centers. I once 

 heard of a mouse falling into a jar of iron sulfate and being converted com- 

 pletely into pyrite. I think we have here an analogue caused by vegetable 

 matter. I feel that many other pyrite or marcasite concretions may have been 

 formed in a similar manner. As to the original source of the iron solutions, 

 I have no suggestions unless they came from previously overlying strata. 



titles and abstracts of papers presented at the afternoon session 

 and discussions tpiereon 



demonstration material in geology 



BY HERDMAN F. CLELAND 



iAl)st7-act) 

 This paper describes some demonstration material which the author has 

 found useful in the teaching of geology in the lecture-room and laboratory. 

 It is offered in the hope that some plan will be suggested by which all teach- 

 ing geologists may be able quickly to learn of useful apparatus or models that 

 have been devised and where and how especially desirable specimens of weath- 

 ering structure, ores, etcetera, may be obtained. 



Presented by title in the absence of the author. 



VRYPTOVOLCANIC STRUCTURE IN OHIO OF THE TYPE OF THE STEINHEI2I 



BASIN 



BY WALTER H. BUCHER 



i Abstract ) 

 The Steinheim Basin is a circular structure less than 1% miles in diameter, 



