124 PROCEEDINGS OF THE WASHINGTON MEETING 



dolomitization intervened between the two. Thus the reefs produced by the 

 first disturbance and the shattered areas and fracture lines produced by the 

 second are often either wholly undolomitized or are very imperfectly altered, 

 while the undisturbed limestone about them is uniformly dolomitized. This 

 proves that dolomitization succeeded the first and second periods of disturbance. 

 But a later disturbance involves both the poorly dolomitized areas and the 

 uniformly dolomitized ones, and a later series of fractures cuts the earlier ones. 



Furthermore, the fact that dolomitization never affects the topmost lime- 

 stone layers of the Saint Louis nor any layers of the Pella indicates that the 

 alteration took place prior to the close of the Saint Louis. Now, since the 

 brecciation of the second type is known to have taken place still earlier, and 

 it is known to be confined to the Lower Saint Louis, it seems probable that 

 this shattering may be related to the uplift which brought tbis division to a 

 close. 



The third period of disturbance was by far the most important. To this is 

 ascribed the extensive mashing and shearing effects and the overthrust fault- 

 ing on a small scale so common in the formation. This was influenced to a 

 large extent by the effects, of the preceding disturbances, thereby obscuring to 

 a large degree the evidence of these. That the deformation which produced 

 this is post-Pella, but pre-Pennsylvanian in age, is indicated by the fact that 

 blocks of Pella limestone have been found sheared down into lower beds, and 

 thus preserved at a locality where Pennsylvanian sandstone generally rests 

 disconformably on these beds of a lower horizon. 



The general parallelism of the strike of the faults and of the tilted layers 

 formed at this time with certain anticlines in the region, notably the Benton- 

 sport anticline which trends approximately north 68° west, suggests a common 

 mode of origin of these two types of deformation. 



Presented by title in the absence of the author. 



VOTE OF THANKS 



The following resolution presented by Professor Fairchild was adopted : 



"Resolved, That the sincere and hearty thanks of the Society be extended to 

 the members of the local committee who have made the efficient and satis- 

 factory arrangements for this large and very successful meeting, especially 

 Messrs. T. W. Vaughan and A. C. Spencer, in general charge of the local com- 

 mittees, and the chairmen of the subcommittees, Messrs. L. W. Stephenson, 

 r. S. Smith, F. L. Ransome, Whitman Cross, and E. S. Bastin. 



"Resolved, That the Society express its thanks to the George Washington 

 University for the use of this building as a place of meeting." 



The Society adjourned at 5.20 o'clock p. m. 



