MARYLAND WEATHER SERVICE 51 



vations in the Lower Midland range from 4S0 ft. for Cecil County 

 near Rising Sun, to 740 ft. for Harford County near Jarrettsville, 

 and 850 ft. for Montgomery County near Damascus. The general 

 topography is very uniform throughout the district, and lakes and 

 ponds are absent. Springs are abundant and constant streams of 

 varving size dissect every corner of the district. Greater or smaller 

 flood-plains have been built up along all of the streams, and in those 

 that are least elevated above the mean level of their stream their 

 vegetation is swamp forest. Marshes and other natural grassland 

 formations are absent. The Susquehanna and Potomac are the only 

 streams rising above the Lower Midland and traversing it. The 

 Gunpowder, Patapsco and Patuxent rise in it. 



The Midland Zone ; Upper Midland District. — The Upper Mid- 

 land District embraces portions of Carroll and Montgomery coun- 

 ties, the whole of Frederick and Washington counties, and the east- 

 ern portion of Allegany County. It is bounded on the east by the 

 summit of Parr's Ridge and on the west approximately by the con- 

 tour of 1500 ft. altitude. 



Parr's Ridge is an ill-defined series of elevations ranging from 

 850 to 900 ft. in height. Just west of its southern termination 

 stands the isolated mountain Sugar Loaf, of 1250 ft, altitude. 

 These elevations are separated by the relatively level Frederick Val- 

 ley from the Catoctin Ridge and the Blue Ridge, which traverse 

 Frederick County in a nearly NNE-SSW direction. The floor of 

 the Frederick Valley is from 250 to 500 ft. in elevation, and the 

 highest points of the Catoctin and Blue Ridges reach 1500 to 2000 

 ft. Extending west from the Blue Ridge to North Mountain is the 

 Hagerstown Valley, 20 miles in width. From North Mountain to 

 the Western edge of the Piedmont there is a continuous series of 

 narrow valleys and steep ridges, — Tonoloway Ridge, Town Hill, 

 Polish Mountain, Warrior Mountain, and other shorter ridges. The 

 floors of these valleys range from 500 to 800 ft. in elevation, the 

 ridges from 1300 to 2000 ft. The Upper Midland presents a final 

 stage of physiographic development, the result of which has been 

 determined by the mineralogical character of the rocks of the dis- 

 trict, each of the great valleys, Frederick Valley and Hagerstown 



