Graven Images: New England Stonecarving and its Symbols, 1650–1815 https://www.amazon.com/dp/0819560405/ref=cm_sw_r_apan_glt_fabc_4MZ5GJAQW60HBDK6BJYS?_encoding=UTF8&psc=1
Also be careful with doing rubbings on older stones, photography is a better approach in most cases. A lot of sandstone stones cam shake, and even finger print oils, tape residue, etc can negatively impact older stones.
The same kind of soul effigy/symbolism is on the cover of a neat book talking about early gravestone symbolism: