Smithsonian Report. 1933. — Bassler 



1. Outcrop near the National Zoological Park, exhibiting an unconformity or gap in earth history, with 

 the uptilted granite gneiss succeeded by horizontal beds of Upper Mesozoic sand and gravel. 



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2. Another unconformity near Washington. The hammer marks the boundary line between the Lower 

 Cretaceous Potomac formation below containing land plants and dino.saur bones, and the marine Upper 

 Cretaceous greensands with sharks' teeth and sea shells. 



