262 ILLINOIS ACADEMY OF SCIENCE 
This sandstone is bluish gray, and also contains numerous 
more or less complete tests of Endymionia bellatula. This 
species of Endymionia is not known to occur at any other 
horizon and hence furnishes a reliable guide to the basal por- 
tion of the Thebes sandstone. 
The middle part of the Thebes sandstone formation can be 
studied in good outcrops in the bank of Mississippi River a 
short distance north of the railroad bridge in the town of 
Thebes, and also in the bank of the river about three miles 
north of the latter place. Corresponding strata are also well 
exposed in the railroad cut a short distance east of Thebes, and 
along the Chicago and Eastern Illinois railroad within a dis- 
tance of one mile both north and south of the village of Gale, 
in Alexander County. At the above mentioned localities the 
sandstone is bluish where unweathered, and is coarser grained 
and thicker bedded than the material in the basal part of the 
Thebes formation. The fossils Climacograptus putillus and 
Lingula ovoides are present throughout this formation. 
The upper part of the Thebes standstone outcrops in the east 
bank of Mississippi River, and in a cut along the Chicago and 
Eastern Illinois railroad one-half mile south of Gale, where 
the contact of this sandstone with the overlying Orchard Creek 
shale is well exposed. The material in the upper part of the 
Thebes formation is bluish, rather coarse grained, and occurs 
in layers 4 to 10 inches thick. The fossils are similar to those 
present in the middle part of the sandstone. 
AGE OF THE THEBES SANDSTONE 
Although the Thebes sandstone in this region contains none 
of the species of fossils characteristic of the normal Rich- 
mond or Maquoketa strata, the stratigraphic position of the 
formation lying above the Fernvale (early Richmond) lime- 
stone as it does at Thebes, Illinois, and Cape Girardeau, Mis- 
sour, and below the Orchard Creek (early Silurian) shale, as 
south of Gale, fixes its age as somewhere in the Richmond 
stage. It cannot be very early Richmond inasmuch as the 
Thebes sandstone not only overlies the Fernvale (early Rich- 
mond) limestone, but is separated from this limestone by a 
sedimentary break of considerable length. Judging from the 
numerous, widely separated areas in which the Fernvale lime- 
