Photograph as originally submitted to this page in the Historical Marker Database www.HMdb.org. Click on photo to resize in browser. Scroll down to see metadata.
36" Diameter Drill Core Tablet
Photographer: Sandra Hughes Tidwell
Taken: May 17, 2023
Caption: 36" Diameter Drill Core Tablet
Additional Description: Taken 85 ft. below ground surface from Potsdam Sandstone Edge rock upon which the Soo Locks are constructed. The existence of this ledge rock formation kept Lake Superior 23 ft. higher than Lake Huron & made the locks necessary.
Submitted: May 26, 2023, by Sandra Hughes Tidwell of Killen, Alabama, USA.
Database Locator Identification Number: p726387
File Size: 6.232 Megabytes

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