Peloidal grainstone and pisolite fill crevices on the flanks of several Silurian reefs in northern Indiana, producing intersecting dikes and veins. Internal dike structures and cross-cutting show that the cycle of crevice formation, sediment trapping, and lithification was repeated several times during the life of the reefs. Significantly, where younger dikes cut across older dike material, their walls have sharp boundaries and matching wall structures, showing that each earlier crevice sediment became lithified before the next fracturing event occurred.

The grainstone clasts appear to have been mechanically swept into the crevices and initially lithified by the precipitation of sparry calcite cement around the grains. Most of the crevice fill now consists of calcite or dolomite pisoliths, however, some exhibit concentric structure, suggesting concretionary growth. Other pisoliths exhibit radial structure in which blades of cloudy calcite encroach on peloids and fossil fragments of the grainstones, suggesting growth by replacement. Petrographic evidence thus favors in-situ growth of the pisoliths, and suggests that lithification of the grainstone was completed by this process.

Evidence favoring vadose cementation of the grainstone, or favoring vadose origin of the pisoliths, is absent, and fresh-water phreatic cementation is considered unlikely. However, the repeated alternation of cementation events with marine reef sediment-producing conditions strongly suggests that initial grainstone cementation and pisolith growth occurred under shallow-water marine conditions.

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