52 THE PLANT LIFE OE MARYLAND 



Valley, being underlaid by limestone, the mountain ridges by a 

 variety of non-calcareous rocks. The mountain slopes are of 

 moderate steepness with thin soils, and in many localities with 

 copious rock fragments or boulders at the surface. As in the Lower 

 Midland, springs and constant streams are numerous but swamps 

 are confined to low flood-plains or mountain "coves" with gentle 

 slope, and ponds are absent. The district is drained by the Potomac 

 and by its tributaries the Monocacy, Catoctin, Antietam, Cono- 

 cocheague and Town creeks. The tributaries rise either in Alary- 

 land or a few miles north in Pennsylvania in each case flowing 

 entirely in valleys of the same mineralogical character throughout. 



The Mountain Zone. — The Mountain Zone embraces the valley of 

 Georges Creek in Allegany County and nearly the whole of Garrett 

 County, and is chiefly characterized by the fact that it lies entirely 

 above 1500 ft. elevation. 



The eastern edge of the Mountain Zone is formed by Wills Moun- 

 tain, and by Dans Mountain, nearly level ridges, the former of which 

 varies from 1600 to 1800 ft. in elevation, the latter from 2000 to 

 2882 ft. at its highest point, Dans Rock. Parallel to these ridges 

 and traversing the eastern edge of Garrett County are the Big 

 Savage and Great Backbone ridges, the highest mountains in Mary- 

 land, ranging in elevation from 2900 to nearly 3200 ft. at many 

 points and reaching near Table Rock 3340 ft., the highest elevation 

 in the state. The valley between Dans Mountain and Big Savage 

 is about S miles wide and is drained by Georges Creek, Braddock 

 Run and Jennings Run. The valley falls below 1500 ft. only near 

 the lower courses of the principal streams. The eastern slopes of 

 the Great Backbone Ridge are drained by the Potomac and, as it is 

 true of all the mountain ridges above mentioned, the eastern slope is 

 much steeper than the western. To the west of Big Savage Moun- 

 tain, Garrett County is traversed in a NE-SW direction by succes- 

 sive ridges, — Meadow Mountain, Negro Mountain and Winding 

 Ridge, the maximum elevations of which range from 2700 to 3000 

 ft. West of Great Backbone Mountain is a relatively level plateau 

 about 5 miles wide, of 2400 to 2500 ft. elevation, bounded on the 

 west by ill-defined ranges of hills of 2500 to 2900 ft. The 



