In the TPMP, there are specific areas such as the Rattlesnake Mountain Sill, located in the western part, that has the best exposed sill with medium to fine grained syenodiorite rock in the northern and southern regions of the mountain (Carman, 1994). The textures in these rocks go from a glassy devitrified content to very fine grained on the surface and medium to coarse grained in the center where contact with country rock and fast cooling cannot occur (Carman, 1994). The major minerals contained within these basalts are augite, olivine, Fe-Ti oxides, and biotites which contain compositional zoning, and zoning in feldspar grains and some pyroxenes (Carman, 1994). Phenocrysts occur on the cooled edges of the Big Bend sills which, when present in a magma intrusion, are rather important because the settling of phenocrysts signifies the major factor in differentiation in intrusions (Carman, 1994). However, phenocrysts are very rare in the Rattlesnake Mountain Sill contact rock, but that does not rule out the possibility of flow differentiation that may have reduced the phenocrysts along the borders (Carman, 1994).Plagioclase grains have a bimodal size distribution with the smaller size having a greater plethora than the larger of the two because the larger ones were transported in by…