THE PRE-RICHMOND UNCONFORMITY 521 
the typical Maquoketa fauna with an abundance of Cleidophorus 
neglectus occurs in certain shales immediately superjacent to a lime- 
stone bearing the typical Rhynchotrema capax fauna of the Rich- 
mond, so that the Maquoketa is shown to be at least as young or even 
younger than the Richmond proper. 
The faunal break in passing from the subjacent Trenton horizon 
_to the superjacent Richmond or Maquoketa is sharp, there being 
little or nothing in common between the lower and the upper faunas, 
and the unconformity suggested by this faunal change is confirmed 
by an actual physical unconformity between the strata over a large 
area. 
The locality where the physical unconformity is most conspicu- 
ously shown is in southern Calhoun County, Illinois, on Madison 
Creek south of Batchtown. At this point the typical Richmond with 
its Rhynchotrema capax fauna does not occur, the section being as 
follows: 
1. Maquoketa shale, 75 feet in thickness. In the upper part this 
formation is a very fine-grained clay shale of a light greenish color, 
weathering to an olive green, some layers containing an abundance 
of graptolites. In its lower beds the formation becomes yellower in 
color and more gritty in texture, and in the lowest six or eight feet are 
several harder and still more gritty beds from one to three inches in 
thickness which stand out upon weathered banks by reason of their 
greater resistance. In these harder layers fossils rarely occur, the 
only two genera observed being Leptobolus and Cleidophorus. At the 
very base of the formation is a granular bed one inch or less in thick- 
ness which is filled with examples of Cleidophorus neglectus, besides 
several species of Ctenodonta, a small Orthoceras, several gastropod 
shells, and an occasional fragment of a trilobite. 
2. Red residuary clay, four to ten inches in thickness, in which are 
imbedded numerous angular, fossiliferous cherts. 
3. Kimmswick limestone, +50 feet in thickness. This is a light- 
colored, highly fossiliferous, crystalline Hmestone of Trenton age. 
Its superior surface is very uneven beneath the residuary red clay that 
rests upon it. 
The unconformity in this section is represented by the red resid- 
uary clay lying between the Kimmswick limestone and the Maquo- 
