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RO C K C A S T L E S Little House Mountain, the closer ridge to Lexington, hides a castle on its summit . Where it rises highest, the sandstone bedrock has eroded into a warren of room-sized mini mesas,each rising twenty feet above the ground,separated from itsneighborsbynarrow,windingcorridorsperfectforgettinglostin,playinghide and seek, and imagining yourself lord or lady of a castle. The mesas themselves are flat, largely bare rock, inviting campsites with magnificent views. The sandstones that cap House Mountain and a number of other area ridges were laid down 450 million years ago, when this area was the continental edge; pick up a handful of their component sands from atop your mountain perch and feel grains that have not been loose since the first land plants were emerging from the sea. These were Silurian times; the geologists think that the sandy beaches built up as the ancestor to today’s Atlantic, the Iapetus Ocean, closed and, closing, pushed up mountains that, eroding, poured their sands seaward in sandbanks as massive as those off today’s Hatteras. The easiest place locally to find these sandstones is Goshen Pass,where the Maury has cut a dramatic seven-mile-long gorge a football field wide, and, quadrangle guide in hand, you can trace their track along the narrow roadbed that snakes between the river and the sixhundred -foot-high walls of nearly vertical rock. Here the sandstone has been folded over onto itself, and you see the same strata again and again and again. The stone on House Mountain is much less thick. You can see this cap especially well in winter from Lexington,its near vertical form easily identifiable from afar.Beneath this sandstone cap lies a much thicker layer of limestone and shale buried under the rubble of collapsing sandstone but sufficiently resistant to provide a less precipitous angle of repose for the lower levels of House Mountain. A glance at any topo map of the mountain reveals a similar picture;regularly paced contour lines grow illegibly close as you approach the top of House,a visual indication of increasing verticality and almost all limited to the sandstone cap. The mountain is remarkably small on the state’s geological and topographical maps. You’d think a landmark as massive and important as House Mountain wouldmaintainitsimportanceonamap,butno,itnearlydisappearswhenlooked ROCK CASTLES 17 at cartographically, and its summit, which dominates the western skyline of Lexington,is but two thumbprint-sized daubs of purple paint nearly lost in a sea of washed-out pink. The pink is the agreed-upon color for the Martinsburg Formation , a fossil-rich skirt of limestone and shale that defines House Mountain’s lower slopes. The purple daubs, one dark, one lighter, are geologists’ shades for the mountain’s sandstone summit. Shale is structurally weak, and the Martinsburg Formation is, everywhere in Rockbridge County, folded upon itself in multiple repeating layers and cleaved into a thousand thousand incomprehensible fragments,which,when exposed,are filled with fossils.These detritus-free slopes are hard to find,and rockhounds are loathe to tell their secret sites.I will but say that here and there upon the mountain’s lower slopes are fields of fossils,stones filled haphazardly with the remains of animals that perished four hundred million years ago, before the dinosaurs, before the reptiles, before land animals or plants, back when trilobites were king. I have found trilobites as small as my little finger, as large as my hand, some entire but most fragmentary, their lobed heads and segmented abdomens littering the rock in places I have divulged only to family. Accompanying them are fragmentary crinoids, sedentary starfish impaled upon star-shaped trunks,so that a bit of seabed seems a petrified fragment of the Milky Way thrown to earth for my delight.Brachiopods are the most commonly preserved residents of these muds,their shell-like head gear resembling a clam closed in upon itself or, if presented in profile, a comma etched against a gray background,palm-sized fragments of long dead reefs making paper weights excellent for dreaming on when trapped at work. If I climb higher than these fossils, struggling up from the well-watered hardwood valleys to the drier piney ridges that reach summitward like arthritic fingers—a vegetable succession traceable from Lexington, where the evergreen pine ridges stand out year around against spring green,fall yellow,and gray winter valleys—I eventually reach the first ramparts of sandstone,ten-foot walls that make...

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