RECORDS 81 



distal ends of the arms of Eiicrimis and Platycrimis. The septal 

 suture of Ammonites show striking localized stages, in that a 

 progressive complexity of the septum is traceable in passing 

 from the dorsal to the ventral border which series is comparable 

 to the progressive complexity seen in passing from the young to 

 adult, and from primitive to specialized types in the geological 

 series. Henry E. Crampton, 



Secretary. 



SECTION OF GEOLOGY AND MINERALOGY. 



November 17, 1902. 



Section met at 8:15 P. M., J. J. Stevenson presiding. 

 The minutes of the last meeting of Section were read and 

 approved. 



The following program was then offered : 



A. W. Grabau, Limestone Regions of Michigan. 



Summary of Paper. 



The limestones considered are of middle Devonian age, and 

 constitute the bedrock of the northern portion of the lower 

 peninsula of Michigan. They are of great economic importance 

 on account of their purity. They are chiefly used in the manu- 

 facture of Portland cement, and for chemical purposes. Through- 

 out them isolated reefs are found, which show all the char- 

 acters of modern coral reefs. The corals and coralines are in 

 the place they grew, while on all sides of them the fragmental 

 limestone derived from the erosion of the reefs is found. This 

 constitutes most of the bedded limestone of the region. On the 

 flanks of the reef it has a steep dip, while away from it, the dip 

 becomes low. The bedded limestone shows all the character of 

 sandstones, but runs as high as 96 or even 99 per cent of CaCOj. 



The fossils in the limestones show a mingling of Corniferous 

 and Hamilton types, in the lower beds. A migration from this 

 region to the Ontario and New York region is indicated. 



Illustrated with diagrams and specimens. 



J. F. Kemp, 

 Secretary, pro tern. 



