Mountain and the eastern slope of the Blue Ridge. The Blue Ridge of Maryland is a continuation of the South Mountains of Pennsylvania and extends as a sharply defined range from the northern border of the state to the Potomac river, which it reaches at Weverton. Its crest forms the border between Frederick and Washington counties. The Blue Ridge reaches its greatest elevation of about 2400 feet at Quirauk, not far from the Pennsylvania border. The Blue Ridge in Virginia is not the direct continuation of the mountains so named in Maryland, but of a smaller range, the Elk Ridge Mountains, which adjoin them upon the west and which are pierced by the Potomac river at Harper's Ferry. Occupying the larger portion of this eastern district and reaching to its western border is the Hagerstown Valley, a portion of the Great Valley of the Appalachian Region hitherto described. It has an altitude of about 500 feet at Hagerstown, which increases somewhat to the northward near the Pennsylvania line, but declines considerably in the vicinity of the Potomac river. The Antietam river and its tributaries occupy the eastern section of the valley and the Conococheague river and its tributaries the western, leaving the central portion of the valley somewhat higher than the sides.

The central division, which comprises the Appalachian Mountains proper, is bounded by the North Mountain upon the east and Will's Mountain, near Cumberland, upon the west. Professor H. D. Rogers describes this district as follows in his report of the First Geological Survey of Pennsylvania: “It is a complex chain of long, narrow, very level mountain ridges, separated by long, narrow, parallel valleys. These ridges sometimes end abruptly in swelling knobs, and sometimes taper off in long, slender points. Their slopes are singularly uniform, being in many cases unvaried by ravine or gully for many miles; in other instances they are trenched at equal intervals with great regularity. Their crests are, for the most part, sharp, and they preserve an extraordinarily equable elevation, being only here and there interrupted by notches or gaps, which sometimes descend to the water level, so as to give passage to the rivers [Potomac]. . . . The ridges are variously arranged in groups with long, narrow crests, some

of which preserve a remarkable straightness for great distances, while others bend with a prolonged and regular sweep. In many instances two narrow contiguous parallel mountain crests unite at their extremities and enclose a narrow oval valley, which, with its sharp mountain sides, bears not infrequently a marked resemblance to a long, slender, sharp-pointed canoe."

Among the more important ridges in Maryland west of North Mountain are Tonoloway Hill, Sideling Hill, Town Hill, Green Ridge, Warrior Ridge and Martin's Ridge, the latter reaching 2000 feet and upwards in elevation. They are arranged in groups of three parallel and closely adjoining ridges on the eastern and western sides with more distant ridges in the middle of the district. The drainage of this area is altogether to the southward into the Potomac river. The deeper valleys in the eastern portion of the region have an elevation of about 500 feet in their lower portions near the Potomac river, but they gradually become higher toward the west. Evitt's creek at its mouth near Cumberland has an elevation of about 600 feet above sealevel.

The western division, which comprises the Alleghany Mountains in its eastern half, forms the extreme western portion of the state. This region gradually merges into a high plateau in passing from its eastern to its western border, with gently undulating mountains rising from the surface, which continue beyond the western borders of the state. The leading ranges of this district are Dan's Mountain, Savage Mountain, Backbone Mountain, Meadow Mountain, Negro Mountain, Winding Ridge and Laurel Hill. Heights of 3000 feet and more are reached in Savage, Backbone and Negro Mountains. The streams flow in part to the southward into the Potomac river as in the central and eastern districts, but throughout much of Garrett county the greater number drain to the northward through the Youghiogheny valley into the Monongahela. This division of the drainage has particular interest, since it marks the watershed between the streams which flow into the Potomac river, reaching the sea by the eastern slope of the Appalachian Mountains, and those which flow to the Gulf by way of the Ohio and Mississippi rivers.

GEOLOGY.

The geology of Maryland as well as its physiography shows an intimate relationship to the adjacent areas upon the north and south, so that its complete interpretation can be gained only by taking into consideration the great eastern border region of which the state is not only geographically but geologically a part. Frequent reference will therefore be made in the succeeding pages to the general distribution and relations of the geological formations found represented within the limits of the state, although the detailed descriptions will be confined to those features more particularly characteristic of the Maryland area.

The state of Maryland is so situated as to display, in spite of its comparatively small size, less than 10,000 square miles of land area, a remarkable sequence of geological formations. The most ancient rocks which make up the earth's crust as well as those still in the process of deposition are here found, while between these wide limits there is hardly an important geological epoch which is not represented. It is doubtful whether another state in the Union contains a fuller history of the earth's past. To make the completeness of this record in Maryland somewhat more intelligible it is well to consider the basis on which geologists are able to determine the succession of deposits.

Geology in its broadest aspects must be regarded as the science of the earth from its very earliest beginnings down to the present day, and as such stands in close relationship to the science of astronomy in its study of the origin of the solar system. In the absence of a more satisfactory theory, most geologists to-day are prepared tentatively to accept the nebular hypothesis of Kant and Laplace as a starting point in earth evolution. This hypothesis supposes that the nebulous, gaseous mass out of which the planetary bodies were formed embraced the most distant orbit of the solar system. As condensation began, successive rings were thrown off, which by further condensation produced the several planets of our system. These in turn may also possess rings or satellites, as with Saturn, or these rings may condense to form a single satellite, as in the case of our Moon. The natural