96 HISTORICAL SKETCH

as a prerequisite to detailed geologic mapping. Since 1883 the topo-
graphic mapping has been extended from time to time, until it now
covers, either in completed or preliminary form, an area of 7100
square miles, or about 75 per cent of the state, while geologic work
has been prosecuted along one line or another with varying degrees
of activity to the present year. A more detailed review of these opera-
tions is given in the following pages.

In addition to the topographic and geologic work above referred to,
mention should also be made of the hydrographic work done in the
state, systematic measurements having been conducted on the Potomac
river and its tributaries and on some of the smaller streams flowing into
the Chesapeake Bay.

The statistical compilation of the mineral resources of the state
should also be noted. This has been conducted yearly since 1882 and
annual reports published. In these reports the coal, brick, pottery
clays and building stones, of which Maryland is such an important
producer, receive a large share of attention, and added to these are
the statistics of iron ores, soapstone, tripoli, slate, etc., all going to
make the report a highly useful one to the state.

Much increased activity has been manifested by the United States
Geological Survey in Maryland since the organization of the State
Geological Survey, it being the aim of the National Survey to aid
those states which show a sufficient interest in the investigation of
their resources to establish official surveys of their own. As the result
of this co-operation between the National and State Surveys the
geology and mineral resources of Maryland will receive thorough
investigation.

TOPOGRAPHIC WORK.

Prior to the commencement of work in Maryland in 1883 by the
United States Geological Survey, the only maps of the state were
those prepared by private individuals, and were little more than dia-
grams of roads. Upon these maps the roads were shown in consider-
able detail, and as a rule not inaccurately, but the maps made little
attempt to represent the streams and none whatever to show the relief.
They were therefore of little service for either scientific or industrial
purposes.