358 ILLINOIS STATE ACADEMY OF SCIENCE 



fully from typical outcrops. These samples were taken 

 from every different layer of the exposure being sampled, 

 and in some cases this has meant a sample every six 

 inches or less. The samples of the limestones were 

 blocks about 3 by 6 by 1 inches, and in ease of the 

 shales, sufficient fragments to make up a corresponding 

 amount. 



The microscopic study of Illinois sediments is just be- 

 ginning. The washing of shales has been tried with both 

 satisfactory and unsatisfactory results. The sandy 

 shales of the Chester formations seem to be practically 

 barren of minutia and so do also some of the dense si- 

 liceous limestones. On the other hand granulated sam- 

 ples of some of the coarser grained, more fossiliferous 

 limestones have yielded a number of small forms which, 

 though they have not been and may not be established 

 as diagnostic, at least hold out a hope for such results 

 with further work. Up to the present time the thin 

 sections made are mainly from the lower Chester 

 formations, and it is quite possible that some of the 

 bryozoa and foraminifera which appear therein may 

 prove later to be diagnostic of these formations. 



As yet no definite course has been pursued with ref- 

 erence to the detailed study of the lithologic character- 

 istics of the samples. This feature is so variable from 

 place to place in many of the formations that at the pres- 

 ent time its use for "long distance" correlation is looked 

 upon as corroborative rather than determinative. 



The amount of work done on the minutia of the Paleo- 

 zoic rocks such as are being studied here in Illinois is not 

 so extensive as that devoted to the younger and less con- 

 solidated sediments. However, the fact that so much of 

 the bed rock of the State is obscured by drift rather urges 

 an attempt to make use of all possible means of subsur- 

 face correlation, and it is hoped that the future work 

 will show results as worth while as those from the 

 younger formations. 



