Between 11,000 and 16,000 years ago the ice of the Wiconsin glacier here at Rockwood was a km thick. As it grew, the great glacier worked like a bulldozer, smashing everything in its way. The glacier was so large, it went from the Rocky Mountains to Newfoundland. Rockwood’s caves and cliffs were carved out as the Winconsin glacier retreated and melted. The power of the fast-moving meltwater streamed down from the glacier, wearing away the softer stone and creating cracks. Over time, these turned into depressions and caves within the rock like you will find here. Left behind was bald limestone and water at Rockwood, as well as all of the interesting rock formations that are visible here today.
Limestone is a sedimentary rock, and along with shale, is one of the best preservers of fossils. Over time, sedimentary rock presses down around what were once living things to preserve the basic outline of their appearance and physical characteristics. Crack open a large piece of limestone or walk a beach covered with limestone rocks and you are almost guaranteed to find a fossil. If you don't find one, rest assured that they are there, lending the calcium carbonate from bones, exoskeletons and shells to the limestone itself. Rockwood Conservation Area is filled with Limestone rock formations. As you walk along The Pothole Trail/Gilbert MacIntyre Memorial Trail you will come along a cave/depression within the rock wall along the side of the trail. If you examine around the cave opening here you will find various fossils embedded within the rock itself. Take a close look to see what you find. Various types of fossils commonly found in Limestone are as follows:
Crinoids
Crinoids are often called sea lilies, but they are animals, not plants. Complete crinoid fossils bear a strong resemblance to flowers. Their stem of small calcite disks are stacked like poker chips, and five feeding brachioles, or arms, extend from the top and resemble flower petals. The oldest crinoids are around 490 million years old and their relatives include sea cucumbers, sea urchins, starfishes and other echinoderms. After the animal died, its calcite disks would fall apart and scatter around the sea floor. Today, these incomplete crinoid parts are commonly found in lumps of limestone. Crinoid fossils appear as discs (when they are flat) or slightly rectangular (when they are fossilized on their side. Some of the discs may still be connected.
Ammonites
Ammonites are creatures with hard shells that lived in the ocean millions of years ago. These animals are the ancestors of octopus, squid, cuttlefish and the nautilus, and look a lot like today's nautilus, even in fossil form. The earliest ammonites lived 415 million years ago. They moved by jet propulsion and had shells comprised of multiple linked chambers. Their tentacles extended outward from the head chamber to catch and devour their prey. As the ammonite grew, new chambers would grow behind the head. Fossilized ammonites often display what are called "sutures," intricate patterned details on the outer surface of the shell that mark where the chambers met the outer wall of the shell. Not all ammonites are round. Some are straight, but still display distinct chambers along the shell.
Trilobites
Trilobites are arthropods, the ancient ancestors of lobsters, shrimp, barnacles, mosquitos and cockroaches. Trilobites appeared in the Cambrian period and were extinct before the appearance of dinosaurs. A mineralized dorsal exoskeleton is the most common fossilized trilobite, and it is usually found in pieces, where they fell as the animal shed it. Complete skeletons are found when an animal died and was buried whole. Trilobite fossils resemble large bugs or lobsters, but they lack the distinction between different sections of their body. When found in individual pieces they are carefully reassembled to form the creature's entire exoskeleton, but if an imprint is found, the surrounding rock is removed to uncover the whole fossil.
Tasks and Logging Requirements
Examine the limestone rock closely, either outside or inside of the cave.
** Please take only photographs and not samples. Examine the fossils by sight and touch but please do not try to remove or damage them in any way.
1) Can you find each of the above 3 types of fossils mentioned?
2) What is the longest measurement of each type of fossils that you found?
3) Which of the above 3 types of fossils are most prevalent?
4) Are certain types of fossils grouped together or are they all just mixed among each other?
Email me the answers to the above questions and then go ahead and log this earthcache. Feel free to post pictures too.
** Please note that there is a fee to enter Rockwood Conservation Area. See additional waypoints for entrance location.