Port Deposit Gneiss

Port Deposit Gneiss Stratigraphic range: Paleozoic
Polished slab of the Port Deposit Gneiss, about 10.7 cm wide
Type	metamorphic
Lithology
Primary	gneiss
Location
Region	Piedmont of Maryland
Extent	eastern Maryland
Type section
Named for	Port Deposit, Maryland

Photomicrograph of Port Deposit Gneiss, approximately 0.85 cm across, under crossed polarized light.

The Port Deposit Gneiss is a Paleozoic gneiss formation in Harford County, Maryland. It is described as a "Moderately to strongly deformed intrusive complex, chiefly composed of quartz diorite gneiss. Rock types include gneissic biotite-quartz diorite, hornblende-biotite-quartz diorite, and biotite granodiorite, with minor amounts of quartz monzonite and hornblende-quartz diorite. Moderate protoclastic foliation grades into strong cataclastic shearing."^[1] It intrudes into the Volcanic Complex of Cecil County.

Quarrying

The Port Deposit Gneiss has been quarried along the west bank of the Susquehanna River for over 100 years.

Port Deposit Gneiss was used in:^[2]

• Many houses and five churches in Port Deposit
• Schools like the U.S. Naval Academy, Haverford College and The Catholic University of America
• Fort McHenry, Fort Delaware and Fort Carroll
• Public buildings like the Boston Public Library and the U.S. Treasury Building
• Public works like the Concord Point Lighthouse, Lincoln Tunnel and the St Augustine seawall

• 
  McClanahan "Granite" Quarry c. 1898
• 
  McClenahan Quarry c. 1910.

References

1. Geologic map of Harford County, Owens, James P., and Southwick, David L., 1968. Scale: 1:62,500. County Geologic Map CGM-1.
2. A History of Maryland’s Lower Susquehanna Region