Experts call the second layer the Fenestrate Bryozoan-Brachiopod Zone. Named for the predominant fossils found there, this layer contains many of the same corals and brachiopods as the Paraspirifer Acuminatus Zone. Here one also can find crinoid stems in abundance. Crinoids are animals that looked like plants, sporting "roots" and "flowers." When the crinoid died, the body segments separated and fossilized, leaving small, doughnut-shaped segments. Prehistoric man used these very popular fossils, which are often called "Indian beads," to make necklaces.

A six-inch-thick layer called the Brevispirifer Gregarius Zone follows, and contains fossils of brachiopods and gastropods (sea snails). The smallest horn corals, or cup corals, begin to appear here. One of the Falls' most unusual corals, called a stromatoporoid, first appears in this layer. Scientists haven't yet reached a verdict on exactly whether the stromotoporoid is a reef-building colonial coral or a sponge, but the creature played an important role in the makeup of the fossil bed.

The Amphipora Ramosa Zone, commonly called the Cave Zone, attracts attention for reasons other than the matlike stromotoporoids or the branching corals. Pocket caves have developed here due to the powerful erosive powers of the Ohio River rushing across the rock. This zone occurs along the vertical cliffs of the river channel, where the cutting force of the river reaches its peak. When water and oxygen come into contact with the limestone, a weak carbonic acid forms and dissolves the limestone. This phenomenon, combined with freeze and thaw erosion and the sweeping power of the river, causes the bedrock to erode quickly and erratically, leaving shallow caves where the rock once lay.

The oldest and most remarkable layer is the largest to be exposed. It bears the name Coral Zone because of its abundance of fossil corals - so many, in fact, that visitors find it difficult to walk on this layer without stepping on fossils exposed in the bedrock. Scientists, geologists, paleontologists, and curious explorers have flocked to the Falls Coral Zone since the 1790's. Explorers here often find upright solitary corals, branching corals, stromotoporoids, brachiopods, a colonial coral called pipe organ coral, another called honeycomb coral, and hexagonaria (known as "Petosky Stone" in Michigan). The largest of the horn corals (Siphonophrentis elongata) sits in this layer and approaches four feet in length. Some of the "coral heads" of the colonial corals measure six to eight feet in diameter!

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