REPORT OF THE STATE GEOLOGIST. lxiii 



The life of this period was abundant. Besides the plentiful remains 

 of various shell fish, crustaceans, and f ucoids, we have great beds of 

 fossil sponges. Its economic importance is due to the beauty of its 

 marbles and its ores of lead. 



The lead deposits belong principally to this system (Silurian), and 

 while exact correlation can not be made on the basis of present knowl- 

 edge, the close relationship to the galena limestones of Missouri, Illi- 

 nois, and Wisconsin is proved. Therefore, the prospector for lead has 

 to watch the occurrence of the rocks described under this system, and 

 having familiarized himself with them, he can confine his work to lo- 

 calities in which he finds them outcropping, and thereby save himself 

 much useless labor, and it is possible that systematic prospecting will 

 bring to light large and valuable deposits of this ore in the limestones 

 of this period. This period, like former ones, was also subject to earth 

 movements, and after its close a great movement broke it in various 

 lines along a trend north 25 degrees east. 



DEVONIAN SYSTEM. 



The beds above these, which are found to consist of j^ellow shaly 

 dolomitic material, have fossils which are closely allied to Devonian 

 forms, and the strata are therefore so classified, subject to the final con- 

 clusions based upon the facts to be ascertained during the coming field 

 season. 



CARBONIFEROUS SYSTEM. 



The exposures of the formations, from the beginning of the Archaean 

 through the Devonian, are confined, so far as critical study has gone, to 

 the Central Mineral Region. To the north and west of this we have a 

 great series of the later Paleozoic sediments which are now exposed, 

 principally at least, by the erosion of the Lower Cretaceous strata 

 which at one time overlaid them. 



In most places the rocks found underlying those of the Carboniferous 

 belong to the Silurian or even older systems. This is the case not only 

 in the eastern border but on the eastern side of the Franklin Mountains ; 

 and on the mountain at Eagle Flat the Upper Carboniferous limestone 

 rests directly upon the upturned edges of the Texan schists. This con- 

 tact with the underlying rocks is always unconformable and often shows 

 the folding and even erosion that took place before their deposition. 



So far as we now know, the Devonian, which is the system immedi- 



