Local structural conditions seem to have had little influence on the concentration of oil in this field. The area is an undulating monocline with a general dip to the west of about 35 feet to the mile. On the north and east sides of the field the oil-bearing sand grades in a short distance into an impervious shale, and this impervious shale prevents the oil from traveling farther up the dip. On the west and lower side of the field the oil is in contact with salt water. The oil production from each well also seems to be in proportion to the porosity of the sand in the immediate vicinity of the well, and has little if any relation to rock deformation. The shale barrier north and east of the field, therefore, has been the medium which retained the oil in its present position and the porosity of the reservoir rock in the vicinity of each well has regulated that well's daily and ultimate production.