Stone, concrete or granite monuments not less than thirty (30) inches in length and four (4) inches X four (4) inches dimension shall be placed along the street right-of-way line at all street intersections, where streets intersect plat boundaries, at all points where there is a change in direction, angle points, or changes in curvature, and at such other locations as the Planning Board may designate. The top of the bound shall be set at the new finished grade.