54 



cracks, which have checkered the surface into roiiglily hexagonal areas. The ex- 

 istence of mud cracks in limestone is a valuable note. In the American (reoio- 

 gist, Vol. IV., No. 6, is an engraving of a slab of Cincinnati limestone, showing- 

 mud cracks. The specimen was found by Prof. ('. W. Hargitt near Moore's Hill, 

 and is now in tlie Moore's Hill College. The association of nuid cracks and wave 

 marks in the same ledge is, no doubt, a valuable note in working out the condi- 

 tions which gave rise to alternating sediments of limestone and shale. Tiic wave^ 

 marks are evidence that the sea was so shallow that slight undulations touched 

 bottom. The mud cracks are evidence of some form of land, a low tide island, at 

 least. The two together seem to sliow a marke<l sliallowing of the sea during the 

 history of one limestone stratum, or a transition from lime-depositing to shale- 

 depositing conditions. 



The other wave-marked stratum to be described presents a surface of exposure 

 about 100 feet by 50 feet. The waves are about three feet from crest to crest, and 

 the hollows are about three inches deep. These wave marks differ from those of 

 the other three strata in that tliey are curved like rainl)OWS. These curved waves 

 are evidence that the undulations of water that caused them were modified by. 

 neighboring shoals or land, the results of a shallowing sea. i 



In this paper I have given only certain facts of structure and have assigned. 

 what I believe to be the immediate causes of these structures. The great problem 

 of the Cincinnati formation is the iuvarial)le alternation of limestone and shale 

 strata. Tiie structure noted may be helpful in working out this prolilem. 



Structural Geologic Work of .1. H. Means in Arkansas. ^By .T. C. 

 Branner. 



Correlation of Silurian Sections in Eastern Indiana. By V. F. Mar,*- 

 TERS AND E. M. Kindle. 



Some New Indiana Fossils. By C. E. Newlin. 



FxTiNCl' Fauna (F Lake County. By T. II. II.vll. 

 ' Tile object of this [laper is to jiresent, S(t far as is known, .some account of 

 animals, supposed to be native, tliat no longer are found in tiie county t>f Lake. 



1. I may as well name first one lliat lias surely been e.xtinct (juite a number 

 of vears, the mastodon, remains of which were foiinil near an old beaver dam 



