the most part by the Potomac, the Patuxent, the Patapsco, and the Gunpowder.
The most conspicuous feature of the Atlantic Plain of Maryland is Chesapeake Bay, which has about two-thirds of its 200 miles of length within the State. It is from 10 to 40 miles wide and its numerous estuaries cut the plain in every direction and reach to the eastern edge of the Piedmont Plateau. The bay is navigable for the largest ships, and its numerous arms furnish a large number of fine harbors. The large area of sheltered, shallow, inland water gives an excellent fishing ground and an opportunity for oyster gathering and oyster culture scarcely equaled elsewhere in the world.
The Piedmont Plateau extends from the edge of the Atlantic Plain to the Catoctin Mountain, the first range of the Appalachian system. This region is about 65 miles wide at the north and 40 miles wide at the south. Most of the surface is broken and hilly, ascending with complicated drainage systems to Parr's Ridge in Carroll County. Between Parr's Ridge and the Catoctin Mountain is the comparatively level Frederick Valley, drained by the Monocacy River, flowing southward into the Potomac. Near the mouth of the Monocacy, the Sugar Loaf Mountain (1250 feet) rises abruptly from the plain. From the Catoctin Mountain to the western boundary of the State, the Appalachian region spreads a succession of valleys, separated by nearly parallel northeast and southwest mountain ranges, and all draining into the Potomac. The Blue Ridge, 2400 feet high at Quirauk, near the Pennsylvania line, crosses the State to Weverton on the Potomac, and is the eastern limit of the Great or Hagerstown Valley. This valley is bounded on the west by the North Mountain, between which and Cumberland is the Alleghany Ridge, a complex chain of long, narrow, very level mountain ridges, separated by narrow valleys, beginning at an elevation of about 500 feet at the Potomac. Just west of Cumberland rises Dan's Mountain (2882 feet). To the west of it is the Alleghany Plateau, giving the elevation of 2000 feet or more to all of Maryland to the west, except the immediate valleys of the Potomac, Savage, and Youghiogheny rivers. Much of the plateau is above 2500 feet, and the highest mountains, the Savage and its extension, the Backbone Mountain, exceed 3000 feet in elevation.
For Flora and Fauna, see those topics under United States.
Climate and Soil. The climate of Maryland is one of transition in which the northern frozen winter gives way to the open southern winter. The extreme temperatures of more northern locations are occasionally met with, but the periods of cold are of less duration and the number of freezing days and the amount of snowfall are less. An extreme winter temperature of 26° below zero has been recorded at Sunnyside in the Alleghany Plateau and a summer temperature of 109° F. near Cumberland. Changes of temperature are frequent, and there is a great daily range. In north central Maryland the average temperature for January is 30°; that for July 75°. The average annual temperature for the State is between 53° and 54°. The average dates for first and last killing frosts in the plateau are October 1st and April 15th; on the Marine Islands the growing season is a month longer, extending from April 1st to October 15th.
The average rainfall for the State is 43 inches, of which 11.5 to 12 fall in spring and in summer and 9.5 to 10 in the fall and in winter. The effects of elevation and slope are clearly shown in the distribution of the rainfall. The western slope of the Alleghany Plateau receives 53 inches; the eastern slope of Parr's Ridge over 45; the inclosed valleys between Cumberland and Hagerstown and small sections at the extreme east and southwest of the State receive between 30 and 35. The Atlantic Plain in the main receives from 42 to 48 inches. The snowfall averages 25.4 inches for the State, 16.6 for the southern and 43.4 for the western districts. The number of days of precipitation on the coast is 130, in the mountains 140. The relative humidity varies from 80 in the sea islands to 65 at the extreme west. The climate is everywhere suitable to tree growth; hard woods, especially oak and hickory, predominate. The warm moist climate and light soil of the eastern shore cause that district to be the home of many southern plants not found elsewhere in the same latitude.
Maryland has a variety of soils corresponding with the geological formations. The more recent formations of the Atlantic Plain have light, sandy and loamy soils, unsuited to grass, but especially adapted to vegetables, truck-farming, small fruits, and peaches. The region of metamorphic rocks and the limestone and shale valleys of the west are of heavier, often clay, soils, usually very fertile and adapted to wheat, maize, grass, and clover. On the western slope of the Blue Ridge Mountains, the Cambrian (Harper's) shale, crossing the State from Harper's Ferry northeastward, produces a strip of sandy, shaly soil with exceptional adaptation to peaches, which are here a highly specialized crop. Similar shaly soils are on the flanks of all the ranges, and the valley floors are usually limestone.
Geology. Maryland presents a great variety of geologic formations, owing to the fact that the various outcrops which run in broad bands parallel with the Atlantic coast are here so narrow that the whole series is encompassed by the State, from the coastal plain formation to the western coal fields, while farther south they widen out so that even the State of North Carolina does not include them all. The entire portion of the State east of Chesapeake Bay and a strip from 5 to 20 miles wide along its western shore are covered with the recent unindurated coastal plain formation, consisting of Tertiary sands and clays east of the bay, and chiefly Cretaceous, with some Eocene deposits, on the western shore. West of this follows the Archæan belt of the Piedmont Plain. It is here about 50 miles broad, occupying the whole central part of the State, but in early Mesozoic time this Archæan land was divided into two parts by a narrow arm of the sea running southwestward from the present mouth of the Hudson, and whose bed is now filled with a deep layer of Triassic red sandstone occupying the Frederick Valley. The narrow western part of the State is traversed by the various outcrops brought to the surface by the Appalachian upheaval and subsequent denudation. They are chiefly Devonian and Silurian strata, more or less tilted and
