Loudoun summers, as a rule, are long and agreeably cool, while
occasional periods of extreme heat are not more oppressive than in
many portions of the North. The mountains of Loudoun have a delightful
summer climate coupled with inspiring scenery, and are well known as
the resort of hundreds seeking rest, recreation, or the restoration of
health. This region, owing to its low humidity, has little dew at
night, and accordingly has been found especially beneficial for
consumptives and those afflicted with pulmonary diseases. The genial
southwest trade winds, blowing through the long parallel valleys,
impart to them and the enclosing mountains moisture borne from the far
away Gulf of Mexico.


GEOLOGY.

The geology of more than half the area of Loudoun County has received
thorough and intelligent treatment at the hands of Arthur Keith in his
most excellent work entitled "_Geology of the Catoctin Belt_,"
authorized and published by the United States Geological Survey.[5]

[Footnote 5: Credit for many important disclosures and much of the
detail appearing in this department is unreservedly accorded Mr. Keith
and his assistants.]

Mr. Keith's analysis covered the whole of Bull Run Mountain, the
Catoctin in its course through Virginia and Maryland to its
termination in southern Pennsylvania, the Blue Ridge and South
Mountain for a corresponding distance, all intermediate ridges and
valleys and contiguous territory lying outside this zone and
paralleling the two flanking ranges.[6]