Just here it may not be amiss to refer to those broad, wholly enclosed valleys whose meandering streams are often bordered by rather marshy ground. Such valleys are known in Garrett County as Glades, while any valley which has steep bounding slopes and slightly marshy flood-plain is called glady country.
These poorly drained areas are calculated to attract attention in a district where the sharp relief of the country in general insures unusually well-drained soils. To one familiar with the poor drainage of the glaciated districts of the United States, glaciation at once offers itself as an explanation of this topography. There are, however, none of the other signs of glaciation, such as transported boulders, striated ledges or morainic material. Moreover, it is possible to adequately explain the Glade Country by appealing to processes acting there at present and during the past.
The following explanation, based on recent geological studies in the Glade districts, is offered by Mr. A. C. McLaughlin of the Maryland Geological Survey:
“The typical Glades of Maryland are located on the strip of Jennings and Hampshire shales which lies between Backbone Mountain and Hoop Pole Ridge in the vicinity of Oakland and Deer Park.
“This broad, gently rolling valley is drained by two rather sluggish streams known as North Glade run and Green Glade run, both of which unite beyond Hoop Pole Ridge to form Deer Creek, a tributary of the Youghiogheny. Hoop Pole Ridge is a monoclinical ridge of Pocono sandstone which offers considerable resistance to erosion and has retarded both of the streams crossing it. While thus retarded at the edge of the Glades by this sandstone ledge, the headwaters of these streams have been working on the yielding shales until they have been reduced very considerably, in fact, quite to the level of the stream crossing on the sandstone.
“The stream grades are now so flat here that they cannot carry away the debris washed by the rains from the low shale hills. The result is that immediately along the streams the accumulation of alluvium has been so rapid that the stream is slightly choked and has thus become marshy. The Glades therefore are simply a well-reduced local base-level plain determined by the marked contrast between the yielding shale and the investing barrier of resistant sandstone.
“It might be added that possibly the inability of the two streams to remove the alluvium may be due to decreased volumes, resulting from recent captures by the headwaters of the Savage or the Youghiogheny rivers, both of which have tributaries on the shales in the immediate vicinity of the Glades.”
excerpt from “A general report on the physiography of Maryland,” Cleveland Abbe, Jr, 1898 PhD dissertation from Johns Hopkins University online at: www.archive.org/stream/cu31924000080691/cu31924000080691_djvu.txt