244 REPORT ON EPIDEMIC DISEASES OF WEST VIRGINIA.

Frost occurred every month in the year; the latest average time in spring is 26th May; and the earliest average time in fall is 23d September.

Aurora Borealis occurred during the twelve years only twice, August 28, 1859, and September 2, 1859.

REPORT

ON

CLIMATOLOGY AND EPIDEMIC DISEASES OF THE DISTRICT OF COLUMBIA.

BY

THOMAS ANTISELL, M. D.,

DISTRICT OF COLUMBIA.

REPORT ON THE CLIMATOLOGY AND EPIDEMIC DISEASES OF THE DISTRICT OF COLUMBIA.

IN presenting this report to the Association, the writer has felt considerable diffidence and embarrassment, owing to its meagre information and shadowy outline; to present for a certain year the historical notice of epidemic diseases of the District when no actual epidemic occurred therein, and when it is impossible to accurately contrast this condition with that of any other year when no official records, municipal or otherwise, have been kept to indicate the nature and extent of disease in years gone by, the embarrassment becomes apparent, and nothing remains as the basis of a report save a notice of the topography and climatic peculiarities, with such remarks upon disease as presented themselves to the experience of the writer or those of his professional brethren whom he consulted.

With this preliminary deprecatory statement the telluric and atmospheric conditions of the District will be noticed.

With boundaries defined by political considerations, the District of Columbia presents to the eye of the geologist no natural features which throw it out into relief distinct from the neighboring States.

Placed at the limit of tidal water of a large river, at a point where in its downward course it has succeeded in cutting its way out of and finally leaving behind a region of crystalline and hard metamorphic gneissose rock, a considerable portion of the present District occupies the site of the ancient river bed which, before it cut its present channel so deeply, once occupied all of the land embraced between Rock Creek on the west and the eastern or left bank of the Anacostia River. Kendall Green, Eckeryton, Kalerama, and Boundary Street formed the shores of this former water course, which, as the water lowered, in time threw a bank between the currents of the eastern branch of the Potomac, forming a sand bank or bar in the shallowing water now known as

Capital Hill; and so by further retiring of the waters and drainage the contour of the surface acquired its present outline.

The whole District, then, east of Rock Creek is underlaid by alluvium consisting of beds of gravel, sand, and stiff clay alternating, the beds of fine gravel predominating. This alluvium is probably from sixty to eighty feet in depth, nearly horizontal in deposition, and, occupying the lower land of the District, makes little mark on its topography. Below the alluvium are pleiocene and miocene beds, chiefly made up of unconsolidated clays or semicemented sand, with few fossils imbedded and none in any state of preservation. These sandy clays and conglomerate pebbles appear at the Maryland line north and east of the District. Through these soft beds both the Potomac and Eastern Branch have cut their way. Along the line of Rock Creek the quaternary beds. disappear, and the alluvium abuts on degraded granite and metamorphic gneiss, which occupy the District thence to its western Maryland border. Heavy clays cover it up in its hollow spots. These metamorphic rocks dip deeply eastward, and on their slope rest unconformably the quaternary and alluvial beds described.

Some parts of the bed of the river Potomac, below Georgetown, are stated to be seventy feet deep, but less than half that would represent its greatest ordinary depth; the clay beds are therefore cut through sufficiently deep to allow of draining of the underground soil, and were it not for the higher level of the plateau in the northern part of and outside of the District, the soil would be exceedingly dry; as it is, much of the draining of this higher land passes down and soaks the beds underneath the city, accumulating close to the river under what is called the island, and as it can only escape at low tide or whenever the downward pressure of the subterranean water can antagonize the tidal current of the river, during seasons of much rain the strata remain waterlogged for some weeks together. This condition appears to be the chief cause of the malarious diseases of the island; for during spring and fall, especially in spring, the island is affected with intermittent to a greater extent than any other section of the city.

The temperature and rain fall of the District have been thoroughly examined. Meteorological observations extending for years have been taken at several points and within the neighborhood of the District in Maryland. Some of this has been carried out by the Smithsonian Institution, but the great bulk of the observations and almost all on record in print have been made under the control of