Antique 1870s G.W. Gray & Son Geological Map of the U.S. - Isotherms, Temperature & Rainfall (32 x 20")"This highly informative 32" x 20" antique map, titled "Geological Map of U. S. Isothems Temperature & Rain fall," was published by G. W. Gray & Son, a prominent Philadelphia firm established in the late 1860s and recognized for producing one of the most successful atlases. Likely dating from the 1870s, this rare map uniquely combines geological features with climatic data, showcasing isotherms (lines of equal temperature) and rainfall patterns across