Protozoa -- algae, bacteria, fusulinids, diatoms, radiolarians Protozoa are usually not found "by eye," instead are found after the rock has been prepared and observed with a microscope. Precambrian Banded Iron Formations of Upper Michigan and Wisconsin's varved quartzites record an early environment dominated by organisms which produced layered structures called "stromatolites." Early metamorphism converted the layers of sediment (winter runoff) and hematite (organic remains). Some finely varved specimens have been suggested as confirmation for glacial conditions during this time. Protozoa, of course, remain today. In fact, microscopic creatures far outnumber any of the higher orders everywhere on Earth. They just don't fossilize well. Recent work in high acid mine environments suggests that some "odd" metal deposits may have been concentrated by Protozoa. The Keewenaw, Michigan aberrant silver/copper intercrystals may have formed as the result of bacterial concentration of metals. Foraminifers and radiolarians are single-celled floating oceanic plankton which occur in today's oceans in great blooms when the proper nutrients are available. Their dead bodies drift to the bottom and are preserved as chalks and cherts, respectively. Other modern plankton, diatoms and coccothithophores, enter the fossil record after Chicago region rocks were laid down. Index fossils called "Fusulinids" are a type of foraminifer. Receptaculites, a spectacular sun-flower shaped inclusion in Paleozoic rocks was long assigned to sponges, but is now considered a member of the fossil algae. Large, round masses of Receptaculites are found in rocks near Lowell in LaSalle County.