Geology and Mineralogy. 101 



sils are zoned in the Cincinnati Series and with which the 389 

 species found in the state of Indiana have been listed. The chief 

 bulk of the material consists of Bryozoa (176 forms, 18 new) and 

 Brachiopoda (48). The authors do not draw the top of the Mays- 

 ville at the Mt. Auburn but at the top of the Arnheim. They 

 say in part : 



" We do not agree either that the Arnheim should be placed in 

 the Richmond, or that the Richmond belongs in the Silurian. 

 There is no lithologic or f aunal break at this level, at least in the 

 present section. Most of the Arnheim species range without 

 interruption from within the Corryville to the middle Arnheim, 

 and many of them throughout the Maysville. . . . 



"At the top of the Arnheim the rocks are irregularly bed- 

 ded and nodular and almost barren of fossils. At this point 

 limestones cease to predominate and are replaced by soft, argil- 

 laceous shale and thin beds of limestone. Shale predominates 

 throughout the Waynesville, which is 105 feet thick. There is 

 also a marked faunal break at the top of the Arnheim. Not less 

 than 30 species of Bryozoa fail at this point or abruptly become 

 rare. Over 20 species make their first appearance at this horizon. 

 The Waynesville fauna is quite distinct from the Arnheim and 

 shows a change of life conditions. There are also numerous 

 migrants from other regions, especially from the northwest, indi- 

 cating a pronounced epeirogenic movement at this time. At no 

 horizon throughout the Maysville is there any faunal or litho- 

 logic change comparable with the one at the top of the Arnheim. 

 Hence, we maintain that the Arnheim should be classed with the 

 Maysville sediments and that the Richmond should begin with 

 the lower Waynesville. On the other hand, we believe that the 

 Richmond is most intimately associated Avith the subjacent Ordo- 

 vician, both lithologically and faunally, and that it should be 

 retained in the Ordovician System" (p. 8). c. s. 



5. Mud Cracks open under Water ; by E. S. Mookk. — An 

 interesting occurrence of mud cracks, remaining open under water 

 for at least several weeks, was recently observed by the writer. 

 In a small pond, a mile and three-quarters west of Julian, along 

 the Bald Eagle Creek, in Centre County, Pennsylvania, an area 

 at least ten feet in diameter on the bottom of the pond was found 

 to be covered with large mud cracks, wide open. The water was 

 about a foot deep and many of the cracks as much as an inch and 

 a quarter wide. The water was not occasioned by a recent rain- 

 fall, which formed a temporary pond, as water has been seen in 

 this area during different months of the year, although the mud 

 cracks were only recently observed. These were first seen on 

 April 4th, 1914, while passing this pond, but they were again 

 observed on April 29th of the same year and appeared to be in 

 practically the same condition as when first seen. 



Owing to the fact that geologists usually consider that mud 

 cracks cannot remain open underwater for any length of time, 

 this seems to be a rather striking occurrence of this feature. 



