图上画点部分为下白垩纪马迪组下部洁净，渗透的砂岩分布区域。
1·Step 4 - the background is then stippled with a carbide tool sharpened to a needle point.
步骤4 -背景，然后用削尖的点画到一个针尖一硬质合金工具。
2·The virtual displacement method specifies that the sum of the shaded areas is equal to the sum of the stippled areas.
虚位移法规定阴影面积之和等于点画面积之和。