534 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



miles. No such other instance is known in American geology. 

 This cap rock no more deserves the taxonomic rank of a forma- 

 tion than the similar cap rocks over the Elmo and Nyman coals. 

 The writer again would advise that correlations in this geological 

 field be carefully considered, as it is impossible that correct in- 

 terpretations of its stratigrai)hi.c relations can be achieved hy 

 only a few days of reconnoisance work. The statement of Doc- 

 tor F. V. Hayden in Final Report on Nebraska, Page 15, "These 

 Upper Coal Measure rocks seem to be as changeable in their li- 

 thogical characters as those of the Tertiary period. What adds 

 to the difficulty, also, is the fact the same species of fossils, with 

 few exceptions, run through all the beds" has much application 

 even today. 



Condra and Bengtson's report "The Pennsylvanian Forma- 

 tions of Southeastern Nebraska" is difficult to obtain, and their 

 ledge names and numbers will be given as far as they are ex- 

 posed in outcrop in the six counties of the two southern tiers of 

 counties in southwestern Iowa : 



Nebraska City. 12. South Bend. 



Nyman coal. 11. Louisville. 



18. rarkio. 10. Union. 



17. Preston. 9. Meadow. 



16. Burlingame. 8. Forbes. 



15. Fargo. 7. Cedar Creek. 



Nodaway coal. 



The Ashland (13) and Rulo (14) ledges of Nebraska are not 

 definitely known to be present in Iowa. 



PALEONTOLOGY. 



Collections of fossils have been made at Essex, Coburg, Red 

 Oak, also at Pinhook, and the different coal mine dumps near 

 Clarinda. This continued study without greatly increasing the 

 number of species already known has extended the range of 

 many species, so that it may be stated there is no abrupt change 

 in the fauna throughout the whole section. During the greater 

 part of a season a species may be searched for in vain when by 

 fortuitous accident it can be collected by the dozen at a horizon 

 where hitherto it has not been found. This well illustrates the 

 statement made by Doctor Calvin many years ago that the fauna 

 of the Missouri stage is found gregariously in colonies. There 

 has been much difficulty experienced in the identification of spe- 

 cies in the genus Marginifera. Norwood and Pratten in 1855 de- 

 scribed three small species of prodnctids of which Productns 



