Geology
The Museum on the Square should wet your appetite for Mason Geology and the Llano Uplift. One of the more infamous sights is located on the Llano River, as seen from a Kayak. Following is an excerpt which recently appeared in the Mason County News:
"As many Masonites know, Mason County has some of the best exposed and most fascinating geology in Texas. Our rocks include such interesting things as the Pleistocene-age finds in alluvial gravels like the Mammoth tusk in the museum, topaz bearing pegmatite seams found in granitic massives, one-billion year old Pre-Cambrian gneisses and schists, and massive 500 million year old fossils. It is these fossils, known as Stromatolites and Thrombolites, that draw the most interest from visiting geologists as they are some of the best, exposed examples of this type of formation in the world.Embedded into the limestone cliffs on the south side of the Llano River downstream from White?s Crossing, these forty feet tall fossils stand sentinel over the gurgling Llano below. Exposed along a mile and a half segment of the exposed strata in these towering cliffs, the grand display ends where the strata (layers of rock) take a decided dip down at a normal fault. These fascinating formations can be viewed not only in the cliff faces, but also in massive blocks that have fallen into the river and along a rocky, riverside ledge where the strata makes its dip, and also at other river-level locations further downstream.The Mason area Stromatolites and Thrombolites are the fossil remnants of the biogenic activities of ancient colonies of bacteria and other microbes, which thrived in warm, shallow, Cambrian seas at least 500 million years ago. For several tens of millennia, these bacteria and microbes existed together, forming colonies of thin mats that captured sea sediments and calcium precipitated by the bacteria and microbes themselves. New mats formed atop old ones, much as coral does today, slowly forming a variety of solid structures, ranging from high edifices to mounds and sheets. These colonies are more scientifically known as bioherms. Speculations are that at some point the conditions in the shallow sea changed, the bioherms ceased to expand, and sediment covered their calcareous structures. Time and pressure preserved the structures in a tomb of solid rock and eventually the Llano River, possibly following a fault line, exposed them again. Their modern cousins (analogs) can still be found living in shallow waters of Australia and the Bahamas. Another type of Cambrian fossil of interest in this area is the Crinoid. Stalks of these ancient creatures can be seen near White?s Crossing and along the rock shelf about a mile and a half downstream of the crossing. Originally these organisms would have been anchored to the sea floor, rising on segmented stalks to a height of a few inches to a few feet. Terminating in a feathery, palm-shaped feeding fan, these animals would have fed by filtering micro-organisms through this fan. Modern equivalents, while not as numerous as their ancestors and mostly without the stalked stem, exist in all oceans in the form of sea-lilies Recent expeditions to the area to view these fossils have included Rice University and Chevron Corporation.On Sunday, February 15th, a large group of students from the Earth Science Department at Rice University braved chilly conditions to learn about the Stromatolites, Thrombolites, and other geologic curiosities. These 18 students were led by Professor Andre Droxler, professor at the Department of Earth Science and Director of the Center for the Study of the Environment and Society (CSES) at Rice University, on a weekend-long field trip to study the geology in the Hill Country, including the Stromatolites and Thrombolites. They also visited Enchanted Rock, Canyon Lake Gorge, and a number of strata-revealing road-cuts en-route. Also traveling with the group was Dr. Dominique Reynaud and his wife Nina. Dr. Reynaud is a world-renowned glaciologist from the University of Grenoble (France) and is the 2009 Wiess Visiting Professor at Rice University. In the past 20 years Professor Droxler has frequently visited the area around Mason and leads student groups around Mason County and along the Llano River two or three times per year. ?Accessibility of the Stromatolite outcrops opened dramatically 3 years ago when we started to visit these outcrops by kayaking and canoeing?, Droxler mentioned.In late 2008 two groups of Chevron geologists from 4 countries (U.S.A., Denmark, Switzerland, Columbia) visited Mason and paddled the Llano River between White?s and James Crossing. The group, led by Stratigraphers, Jason Francis, PhD, Miriam Andres, PhD, and Megan Murphy-Bishop, PhD, conducted team building exercises and studied the Stromatolite and Thrombolite formations as they relate to oil bearing strata in other parts of the world. While Mason rocks do not bear oil, they do allow geologists to better understand rock formations thousands of feet below the earth?s surface. Stromatolite expert Megan Murphy-Bishop was quoted as saying, ?These are world-class, ?textbook? Stromatolites!?"
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