DEVONIAN OUTLIER NEAR ROLLA. 277 



great numbers of well-rounded quartz nuclei with strong evidences 

 of secondary growth. In some sections the grains show as angular 

 interlocking crystals because of this secondary growth; in 

 other sections, large secondarily enlarged grains are separated 

 from each other by a finely crystalline ground mass of the 

 same material. The rock contains numerous cavities, most of 

 which have been formed by the leaching out of large fossils, and 

 on the surfaces of these cavities are to be found many small but 

 perfect crystals of quartz and of limonite pseudomorphous after 

 pyrite. The quartzite is somewhat fractured, and these fractures 

 are filled with a soft, yellow, non-fossiliferous, somewhat con- 

 glomeratic sandstone. 



From the structure and secondary growth it seems evident 

 that the rock was originally a calcareous sandstone, laid down 

 by. an advancing sea against an old land mass. The calcareous 

 matter has been completely leached out, and much of it re- 

 placed by silica. The soft, yellow sandstone is of later age, 

 either basal Mississippian or Pennsylvanian. 



Paleontology. — Fossils are abundant in the quartzite. They 

 are not evenly distributed, but are most abundant at the base. 

 At the first glance, parts of the stratum appear to be barren, but 

 careful search of almost any fragment will reveal fossils. The fos- 

 sils all occur as external and internal molds, and in most cases 

 the preservation is excellent. Corals and Mollusca dominate 

 the fauna. Other forms are not common, though individuals of 

 a given species may be very abundant. 



The following table gives a ! ist of the species which have 

 been obtained from this quartzite, and also their occurrence at 

 other localities. Column 1 shows species occurring in the Grand 

 Tower formation in southern Illinois; column 2, species occurring 

 in the Jeffersonville beds at Louisville, Kentucky; column 3, 

 species occurring in Michigan; column 4, species occurring in 

 Ohio; and column 5, species occurring in New York. 



