The round feature looks like a laccolith , with a variety of exposed rocks eroding away inside the uplifted area. The uplift explains why the erosion above the laccolith is faster, as it cracked the existing rock and sped up erosion of it. Thus this particular laccolith is a depression rather than a lump. Multiple rings around the laccolith showing the uplift of the rock strata is a strong indicator too.
stocks should be lumps, or circles , of a homegenous igneous rock .. With no sign in the previously existing rock of the stock specifically.