Natural Resources Building - Building Stone

Roof A greenish gray slate covers the roof. It is an excellent roof material for two reasons. One, slate splits along parallel planes of weakness into smooth-surfaced slabs and sheets; this splitting is called slaty cleavage. Two, slate has a fine grained surface that is relatively impervious to water.

Closeup of the roof

The slate was quarried from the Maine and western Vermont slate belt by the Rising and Nelson Slate Company of West Pawlett, Vermont. These slate deposits originated as sea-bottom muds during the Cambrian and Ordovician Periods (more than 450 million years ago). As the muds were deeply buried by younger sediments, they became compacted and cemented into shale, a sedimentary rock. Near the end of the Ordovician Period (438 million years ago), the earth's crust in this part of what is now New England was uplifted to form mountains. Heat and pressure produced by folding during the crustal uplift changed some minerals in the shale to micas and altered the shale to slate, a metamorphic rock.