Plate XXXIV. Continued. 



PAOE. 



5 a. The surface of same x!2, showing its appearance when not abraded. 



!}. The outer portion of a vertical section x!8. 



5 c. Tangential section x!8, showing the characters of the zooecia and meso- 

 pores in the zones where the latter are not entirely filled with the 

 secondary deposit. 



d. Tangential section x!8, showing the appearance where the section 

 passes through one of the solid zones. 

 Trenton limestone, Dixon, 111. 

 E. O. Ulrich's collection. . 



