In a lithologic log, how would a sandstone interlayer within limestone be depicted?

• A. By modifying the limestone symbol to include the sand symbol within its blocks
• B. By drawing separate, stacked layers for limestone and sandstone
• C. By using a single sandstone symbol for the entire interval
• D. By shading limestone with a sandstone crosshatch

Answer: (A)

The idea being tested is how to show mixed lithology within one interval on a lithologic log. When sandstone occurs as interbeds within limestone, you portray the interval with the dominant rock symbol (limestone) and indicate the subordinate lithology (sandstone) inside that block. This is done by modifying the limestone symbol to include the sandstone symbol or pattern within its area. It communicates that the interval is largely limestone with sandstone interbeds, rather than treating them as completely separate, stacked beds.

This approach avoids implying a sharp boundary between entirely distinct layers (which would come from drawing separate stacked layers) and avoids using a single symbol for sandstone (which would erase the limestone dominance). Shading or crosshatching that doesn’t integrate the two symbols could be ambiguous. So the best representation is a limestone block that includes the sandstone symbol inside, showing interlayering within the interval.