MARYLAND GEOLOGICAL SURVEY 497

Emmitsburg and Edgemont would be in Pennsylvania and Hancock
on the boundary. The maximum deviation from Mason's and Dixon's
line—about 2 1/2 miles—would have occurred near Leitersburg and the
west end of the line would be too far south by nearly a mile...

If now a magnetically east and west line were re-run at the present
time, starting again from the east end, the line, as will be seen, would
run considerably south of the true boundary. The rich coal regions
of Allegany and Garrett counties would now lie almost entirely in
Pennsylvania and the west end of the line would be just about at the
middle point of the west boundary line, or in other words about 19
miles too far south!

This illustration brings the fact of the secular change of the magnetic
meridians in the course of one century vividly before the mind.
Fortunately, the Mason and Dixon line was run true east and west,
and hence will be fixed forever.

Now let us suppose that a surveyor were called upon at the present
time to re-run the magnetic east and west line of 1800. Then the
question of proper allowance of secular variation would enter in and
be the dominating factor in the accurate re-running of the line.
Making the most favorable supposition possible, the precise position
of the 1800 magnetic east and west line would never again be regained.
Under favorable suppositions a skillful surveyor might approximate
quite closely to the line, but assuming that conditions exist similar
to those prevailing in the greater portion of the state, even the skillful
surveyor might run a line which would be so far out as to make it
doubtful whether certain towns belonged to this state or the adjoin-
ing ones. His line might be a fruitful cause of litigation for owner-
ship of valuable districts, e. g., the coal regions. This is precisely the
condition of things in many parts of Maryland to-day, hence the prac-
tical importance of making our secular variation data as accurate as
possible. During the present year special effort will be made to
increase our knowledge of the secular change.