Geology Merit Badge Trail     Sedimentary rocks start out horizontal. The slow and gradual movement of the earth's crust can bend, fold, stand these rocks on edge, or even tun them upside down. That deformation has happened in the Ouachita Mountains. It gives structural geologists headaches.   Introduction Plate Tectonics Time Scale and History Formation of the Ouachitas Faults and Earthquakes Fossils Geologic features Environmental Geology Fossil Fuels Careers

A Few Geology Illustrations THE CRUST OF the earth is in slow motion action, constantly being stretched or squeezed. The pressure on the rocks can deform or break them, causing folds or faults. Folds mainly go up and down. The ones that go up are called anticlines, the ones that go down are called synclines. These features can be large enough to be hills and valleys in a mountain range, or can be squiggles seen in a hand-sized rock. In the Ouachita Mountains of Arkansas, the layers, or strata, of the rocks have been so corrugated and convoluted, that interpretation of events causing these deformations cause considerable debate among geologists. In other parts of the state, like north Arkansas, nice nearly horizontal layers of rocks can be seen to extend miles across counties. It shows that different forces work in different places. The layers of these sedimentary rocks leave a record of events of deposition, with each new layer laid down horizontally over older ones. In some time periods no new sediments were added, or changes in the land caused earlier layers to erode away. These events leave gaps in the sequence of the strata called unconformities. An unconformity represents a contact where beds of rock of different ages meet, instead of a continuous history.   The structure of a slope is called its strike and dip. Geologists draw these symbols on maps to define the way beds of rock are at angles, or the way they are dipping. Strike and dip are at right angles to each other. The arrow points in the direction of dip. The angle of dip is the angle (in degrees) off of horizontal that the bed is dipping. It is usually measured with a Brunton compass and is given by a number like 28 degrees or 45 degrees.     Next page is Geology and sources of energy Ch , page 7 Contact the authors of Rockhounding Arkansas revised Feb 2000 ©Rockhounding Arkansas 1998 http://rockhoundingAR.com