Rocks of the Ridge - Cockeysville, MD - Rock and Mineral Displays on Waymarking.com

The sign says:

Gneiss
The oldest rock in Oregon Ridge Park lies 2,500 feet beneath you. It was formed one billion years ago by tremendous pressure and heat deep within the Earth's crust and then was thrust to the surface in mountains perhaps taller than the Himalayas. This metamorphic rock is called Baltimore Gneiss.

Limestone Layers
For hundreds of millions of years the mountains were worn fown by wind and water to a flat plain. Ocean water washed across the plain and formed warm, shallow seas teeming with marine life. Lime-secreting algea and shells of sea creatures drifted to the sea bottom and, layer upon layer, became-cemented together to form limestone. Sand and clay on the sea bed were squeezed into shale and sandstone and stacked up on the limestone like layers of a cake.

Marble and Schist
Another period of movement in the Earth's crust caused the horizontal layers to be stretched, heated, changed, then folded them up in a wave pattern of large domes that form the rolling hills of northern Baltimore County.
Limestone became sugary-white Cockeysville Marble, a prized building stone used in construction of the Washington Monument and the many white steps of Baltimore. The shale became Loch Raven Schist, composed mainly of shiny mica as well as garnet, a semi-precious gemstone.
This rock folding also brought the Baltimore Gneiss to the surface to form the ridge across the valley behind you, north of Shawan Road. Cockeysville Marble, which erodes more quickly than schist or gneiss, lies in the wide, open valley between the two ridges.

Type of Display: Geological

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Date Logged Log   07/16/2023 Searcher28 visited it