"Antique 1870s G.W. Gray & Son Geological Map of the U.S. (32" x 20")This highly informative 32" x 20" antique map, titled "Geological Map of the U. S.," was published by G. W. Gray & Son, a prominent Philadelphia based firm established in the late 1860s. Renowned for producing one of the most successful atlases ("Gray's National Atlas") and for being "one of the last to employ hand coloring on maps," their meticulous detail and distinctive hand coloring are evident throughout. Likely dating from the 1870s, this map