Reef core is massive crinoid-dominated wackestone with large floating stromatopores. 
Some stromatolites.

Other collections from Patzkowsky refer to nearby quarries with similar fauna.
 

Abstract of ref. 1105:
The Racine Formation of southeastern Wisconsin contains a diverse reef fauna of Silurian (Wenlockian) age. A collection of more than 10,000 specimens from this fauna includes 191 species and 38 guilds of reef constructors, binders, bafflers and dwellers. Constructors and binders include stromatoporoids, tabulates, rugosans and bryozoans; bafflers include branching tabulates and dendroid rugosans. Only locally do these groups form a skeletal framework, and for the most part, their remains are separated by reef matrix. Reef dwellers are represented by diverse guilds of brachiopods, gastropods, cephalopods, trilobites and echinoderms, and they also include receptaculitids, sponges, solitary rugosans, bryozoans and bivalves. Tiering within the fauna is well developed and probably extended to a height of 1 m above reef surfaces. This reef fauna exhibits higher species diversity, greater numbers of guilds and more extensive tiering than Silurian level-bottom communities. Relatively few of its taxa, however, are restricted to Silurian reef environments. Constructors, binders and bafflers in the reef fauna have morphologic and taxonomic parallels in level-bottom communities, as do nearly all taxa of reef dwellers. Higher diversity in the reef fauna is not a function of specialized reef guilds and species, but results from packing of more species into the same guilds which are present in level-bottom communities. In this regard, the Silurian reef fauna differs fundamentally from that of today and reflects the generally low grade of ecologic complexity of the Paleozoic evolutionary fauna. 