An
inlier is an area of older
rocks surrounded by younger rocks. Inliers are typically formed by the
erosion of overlying younger rocks to reveal a limited
exposure of the older underlying rocks.
Faulting or
folding may also contribute to the observed
outcrop pattern. A classic example from
Great Britain is that of the inlier of folded
Ordovician and
Silurian rocks at
Horton in Ribblesdale in
North Yorkshire which are surrounded by the younger flat-lying
Carboniferous Limestone. The location has long been visited by
geology students and experts. Another example from
South Wales is the
Usk Inlier in
Monmouthshire where Silurian age rocks are upfolded amidst
Old Red Sandstone rocks of
Devonian age One example from Great Britain is the mass of
Triassic sandstone around the
Staffordshire town of
Leek. This is isolated from the very much larger area of Triassic rocks which characterise the
English Midlands and
Cheshire Basin, to the south and west respectively, by the surrounding
Carboniferous sandstones and
mudstones. Similarly in the
Black Mountains of South
Wales, the summit area of
Pen Cerrig-calch is composed from a suite of Carboniferous age sandstones and
limestone. This outcrop is isolated from the main extent of these rocks (which form the
South Wales Coalfield and its margins some miles to the south) by the
Devonian Old Red Sandstone on which it rests by and by which it is surrounded.
Grenvillian inliers located within the
Appalachian orogeny include the
Pine Mountain Belt in Georgia, the
French Broad Massif along the Tennessee and North Carolina border,
Sauratown Mountain Massif in North Carolina, the
Shenandoah Massif in Virginia, the Baltimore Gneiss Domes in Maryland, the Honey Brook Upland in Pennsylvania, and the
Reading Prong, which extends from Pennsylvania into New York. Other inliers include the Berkshire Massif, which extends from Massachusetts into Vermont, and the Green Mountain Massif in Vermont. Associated Canadian inliers include the Blair River Inlier on
Cape Breton Island, Nova Scotia, the Steel Mountain Terrane on Newfoundland, and the
Long Range Inlier on Newfoundland. In West Africa, the
Kenieba inlier borders southwestern
Mali and eastern
Senegal, and associated
Birimian gold is found in
Kalana and
Sabodala respectively. ==Outlier==