Figure 27. Diagram showing upper Ellerslie Member anticlinal traps caused by differential compaction, Edmonton area, Alberta. (a) Draping of strata above stacked lenticular sandstones lying on uniformly sloping eroded surface of Devonian Wabamun Formation. (b) draping of strata above ancient hill on eroded top of Devonian Wabamun Formation. (c) Draping of Cretaceous strata above Devonian Leduc pinnacle reef.