<p> Microstructural as well as structural analysis of amygdules and groundmass of the Catoctin F·ormation located in the overturned western limb of the South Mountain anticline permit interpretation pertaining to the nature of cleavage development. Various -metliods haye been employed in the structural analysis of amygdules, in order to ascertain their original shapes and also the nature of the tectonic strain ellipsoid. A deformation path has been constructed in logarithmic co-ordinates. This appears to be an improvement over the arithmatic graph of Wood (1974). Microstructural investigation allows recognition of two distinct domains within the groundmass and amygdules : i)an early schistosity and ii)a crenulation cleavage. Microstructural and structural analysis provide a logical explanation of this history. An initial flattening episode forming the early schistosity was followed by approximately plane strain deformation creating the crenulation cleavage. </p> / Thesis / Bachelor of Science (BSc)