37 



in such a way as to show its geological structure and the area 

 occupied by each formation. The geological structure is further 

 shown by numerous measured sections, most of them showing 

 local relations of the strata, but the principal one was con- 

 structed from exposures along the Mississippi river, which forms 

 the whole western boundary of the State. This section shows 

 the relation of the different formations, from the Potsdam 

 Sandstone to the Coal Measures, inclusive, for a distance of 

 more than 600 miles. 



The immense economic resources of the State are also shown 

 in these volumes. The characteristics and outlines of its 37,000 

 square miles of productive coal field are recorded. The lead 

 region has been carefully explored and mapped, and the char- 

 acter of its mineral products determined. Besides this the 

 character of the soils of the State is described; and its re- 

 sources in stone and other building material are shown to be 

 abundant and good. 



The most conspicuous portion of this great work, however, 

 is its palaeontology. This portion is so extensive and elaborate 

 that the volumes of the Illinois survey have long been indis- 

 pensable to every palaeontologist in every part of the world 

 where the palaeozoic formations are studied. The fossil forms 

 described are all well illustrated. They have been collected from 

 all the formations, from the Potsdam Sandstone to the Upper 

 Coal Measures, inclusive: but those of the Lower Carboniferous 

 and the Coal Measures are especially abundant. Some indica- 

 tion of the extent of this palaeontological work is shown by the 

 fact that it embraces the description and illustration of 297 

 species of vertebrates, 1073 species of invertebrates and 256 

 species of plants. Nearly 1.500 of these species were first made 

 known to the scientific world through the publications enumer- 

 ated in the foregoing list. 



Such briefly are the character and extent of the labors of 

 one who for nearly forty years devoted his best energies to 

 their fulfillment. 



