CHRONICLES OF
CENTRAL PENNSYLVANIA MINERALOGY
Part Three
Jay L. Lininger
Dillsburg, PA
DILLSBURG: COULD IT HAVE BEEN ANOTHER CORNWALL?
In Part One of the CHRONICLE series, I discussed briefly the importance of the
Pennsylvania iron industry during the nineteenth century. The development of this vital
industry in our state coincided with the period in history which historians describe as
the "American Industrial Revolution." The Susquehanna Valley was well
represented by an active iron industry which had been established several decades before
the American Revolution. Most of the local eighteenth century workings were comprised of
the familiar "iron plantation" workings surrounding a fire-belching, charcoal
fueled blast furnace. Lacking good roads and a major transportation system forced most of
the enterprises to be situated near the source of raw materials. Thus, most iron producing
furnaces were located near the ore mines, limestone quarries and vast hardwood forests
which covered Pennsylvania. By the dawn of the nineteenth century, hundreds of self
sustaining iron manufacturing complexes could be found throughout the region. The majority
of ore was extracted from the abundant residual limonite deposits which were formed at the
margins of the great sedimentary beds of sandstone and limestone across the Appalachian
arch. Although the limonite was not high grade ore, it was desirable because the deposits
were close to the surface and were often very large in width and length. Ore recovery
could be conducted by the pick and shovel method, and mine shafts were rarely required.
Further east, successful iron mining was also being conducted on
the high grade magnetite deposits which formed at the contact zones of intruding diabase
and older limestone beds. Large mines and furnaces processed the high grade magnetite ore
at Cornwall, Hopewell, Pottstown and Morgantown. In the Susquehanna Valley there were no
known magnetite deposits, but the region was amply represented by dozens of the open-cut
limonite deposits which were described as "ore banks." When the borough of
Dillsburg was founded in 1833, the furnace and ore banks at nearby Boiling Springs had
already been in operation for more than 80 years.
Dillsburg was a village founded at the crossroads of commerce in the northern York
County farming community. Its bucolic setting in the shelter of the South Mountain, and
its fertile and well drained soil gave no hint of the mineral wealth which lay just under
the surface. The science of geology was in its infancy, and knowledge of Pennsylvania's
geology was non existent in 1833. The rapid growth of mining in the Keystone State began
to fuel the desire for practical geological information, so the state legislature
commissioned the First Geological Survey in 1836. The eminent Henry D. Rogers was
appointed as state geologist. Rogers began the awesome task of exploring and interpreting
the vast and complex geology of Pennsylvania. His many years of effort culminated in the
publication of a major work -- the three volume series entitled the GEOLOGY OF
PENNSYLVANIA (1858). This hard to find series is highly prized by serious Pennsylvania
mineral collectors. As Rogers traversed the state, he issued a series of preliminary
reports. One of the early reports (1840) noted that geological indicators in Dogwood
Hollow, near the village of Dillsburg, could be a possible clue to the presence of large
iron deposits. His prophetic comments would be confirmed many years later when large
limonite and clay deposits were discovered and developed in Dogwood Hollow.
What Rogers couldn't know about was the presence of much higher grade iron ore in the
form of magnetite, which lay beneath the fields in the flatlands and rolling hills about a
mile east of Dillsburg. The discovery of this important ore deposit was credited to a
local resident. During the spring plowing in 1847, Dillsburg farmer Abraham Mumper was
perplexed when his plow unearthed some dense black boulders in one of the fields on his
property. His curiosity and expectations were fulfilled when the mineral was identified as
a rich grade of magnetite ore. Although the magnetite contained an excess of sulfur (due
to included pyrite), the percentage of iron was higher than the local limonite ores. More
importantly, local iron masters had learned through experience that a judicious mixture of
limonite and magnetite produced a better grade of boiler plate iron. The ore mixture
produced an alloy of sorts that resisted the brittle cracking brought about by great heat.
That quality was desirable for the manufacture of wood stoves and firebacks.
Abraham Mumper now possessed a commodity that was economically desirable. There existed
a ready market in the Susquehanna Valley because of the many furnaces already in
operation. Mumper could afford to sell the ore at attractive prices. He could eliminate
the long distance shipping costs required for the eastern magnetite ores. He didn't need
to refine the ore; simply mine it and sell it to local furnaces. The economics were
simple. He treated the ore as just another "cash crop," and soon found himself
on the road to prosperity. It is said that imitation is the sincerest form of flattery.
Mumper should have been flattered, because his success spawned an active search by other
residents over the acreage east of town. In time, several more surficial deposits were
discovered. More mines were established, including one by Mumper's brother John. Within a
few years the region began to take on the look of a mining district. This mining district,
however, had one peculiar difference. All the ore was mined and sold by contract to other
furnaces. No furnace or smelting operation was established in or near Dillsburg. This
arrangement would remain in place until the closing of the last mine in 1908.
The magnetite ore at Dillsburg occurred in veins or pods, and was distinctly different
from the residual limonite ore bank deposits so common throughout the lower Susquehanna
region. The early workings at Dillsburg began as open cuts, but eventually were converted
to mine shafts after the easily obtainable ore was exhausted. By the time of Mumper's
death in 1868, he was wealthy, but the open cut mines were past their prime.
Mumper's property was purchased from the estate by his son-in-law Alexander Underwood.
Although Underwood was a practicing attorney in Mechanicsburg, he was well aware of
Mumper's success in the mining business. He was determined to develop the Mumper Mine in a
much more ambitious fashion, and having no practical mining experience, turned to those
who did. He hired the Wrightsville Iron Company to develop the property. Underwood's hopes
were rewarded in 1872 when a large quantity of ore was discovered at a depth of 26 feet.
Seams of pure magnetite up to 18 feet in width were encountered, and three drifts were
developed to recover the ore. At the peak of production, 40 tons of ore per day were
removed.
In the meantime, another attorney by the name of John Logan was struggling with a
quandary of his own making. The Dillsburg lawyer had once been the owner of some land
located in the general vicinity of the newly expanding Underwood Mine. Logan had inherited
the property from his father's estate, and during the initial mining "boom" had
made a thorough exploration of the property. There existed no surface indications of iron
ore, so Logan succumbed to an offer to sell his land to a local farmer. In light of the
development of rich new veins nearby, Logan began to have second thoughts on the wisdom of
selling the property in the first place. In an act considered impulsive by local
residents, Logan convinced the owner to sell the property back to him for a figure
described as "a vastly inflated sum." Logan's risk was turned from folly to
fortune, however, when the same rich vein was discovered on the repurchased property. Is
it possible that the disdain felt for lawyers is not a recent phenomena?
Meanwhile, the study of geology in Pennsylvania became somewhat inactive after the
release of the Rogers three volume series. That would soon change, as the American Civil
War and post war reconstruction pushed the development of iron mining and manufacturing to
new heights. In order to meet the demands for updated information, the State Legislature
was required to commission the Second Geological Survey. The new survey, now greatly
expanded in size, was placed under the direction of Professor J. Peter Lesley of
Philadelphia. The knowledgeable and outspoken Lesley was methodical in his organization of
his staff. Responsibility for the study of specific areas was assigned to the best suited
geologists. Exploration of the iron rich regions of Adams, Cumberland, Franklin and York
Counties were assigned to Persifor Fraser and A.E. Lehman. During the summer of 1874 these
two men made a visit to every iron mine in the four county area, no small task because
there were hundreds of them. In their initial survey report of 1874, the two men
recognized the uniqueness of the Dillsburg magnetite deposits, and determined to revisit
the district for a more detailed study during the following year.
During the latter part of 1873, a nationwide financial depression (known as the panic
of 1873) impacted much of the business community. As a result, many mining operations were
closed or temporarily suspended. The Dillsburg ore fields were no exception. Several of
the ten major magnetite mines were closed during the visit of Fraser and Lehman. Access to
most of the mines was available to the geologists, however, and the report submitted after
their investigation provides us with the most detailed and accurate account of the mines
that was made available by knowledgeable observers.
The economy rebounded in 1876 and most of the operations resumed as before. Over the
next two decades recessions would come and go, but the demand for magnetite ore helped to
keep the Dillsburg mining industry reasonably stable. It was also during this period that
a number of large orebanks were developed in the newly discovered limonite deposits
located west of Dillsburg in Dogwood Hollow. These were the same mineralized zones
predicted by Henry D. Rogers during the studies made for the First Geological Survey many
decades before. The life of these newer mines were prematurely ended with the discovery
and rapid development of the hematite ore masses in the Mesabi Range of northern
Minnesota. Mining continued in Dogwood Hollow for a few additional years because of the
exploitation of white clay deposits which were found in proximity to the limonite beds.
Over in the magnetite ore fields, the large known reserves of high grade ore were
approaching depletion by the turn of the century. Most of the older mines were closed, but
the King and Jauss Mines, located in the southern most portion, were still producing. In
August 1906, a brief flurry of excitement was aroused when the Jauss Mine was visited by
the famous inventor Thomas Alva Edison. Although Edison was well known to the public for
his remarkable inventions, he was also an entrepreneur with investments in iron mining and
cement manufacture in central New Jersey. Edison and his son were escorted to the mine by
John Morris, a local resident with a broad knowledge of the Dillsburg mines. Edison
pronounced the ore to be high grade, but was apparently more impressed with Morris than
with the Jauss Mine. He never invested in Dillsburg mining property, but he did hire
Morris to serve as a mining engineer for a number of his other mining ventures.
Numerous attempts to inject financial resources into the old Dillsburg ore fields were
of no avail. The Jauss Mine closed in 1908, and the district died a quiet death after
producing 1,500,000 tons of ore. An epitaph of sorts was written by U.S.G.S. economic
geologist Arthur C. Spencer. He had been preparing a field report on Pennsylvania's
Cornwall type occurrences, and the timeliness of his investigation (1907-1908) permitted
him to visit the Dillsburg district while several of the mines were still accessible. His
observations provided a clearer picture of the geology of the ore occurrence, as well as
additional information on the mines themselves.
In spite of the mines being closed, there remained an unsettling aura of uncertainty.
Could it be possible that a large amount of ore yet remained? When the district was
active, the mines appeared to be random, covering an area much more widespread than any of
the other Cornwall type occurrences. No systematic exploration or development had ever
been undertaken by a major mining company. Instead, the deposits had been located by
surface indications, or by the use of a dip needle device. This primitive instrument would
show indications of the ore deposits by the magnetic attraction of the needle to deeper
ore bodies. In the years that followed the mine closures, local landowners kept property
intact in the hope that additional ore would once again be discovered. The advent of World
War II set the stage for one final scientific evaluation of the region.
Because of the demands of war for ever increasing amounts of natural resources, many of
Pennsylvania's older mining districts were reevaluated for mineral deposits which may have
been overlooked. The renewed search at Dillsburg was conducted by a team of U.S.G.S.
geologists under the leadership of G.L. Neumann and Preston Holtz. Extensive drilling
throughout the orefield was commenced in 1942 and produced some conclusive results.
Additional ore, estimated at perhaps the same amount already mined, was discovered. The
random nature of the ore pods was confirmed. There existed no large massive orebody such
as was found at Cornwall and French Creek. The ores at those two famous mines represented
a major contact zone between the older limestones of the region and the newer diabase
intrusion producing metasomatic replacement of limestone with enriched magnetite. Holtz's
interpretation of Dillsburg's occurrence pointed to a deep seated diabase intrusion which
included several thin offshoots or sheets of diabase, perhaps of newer origin which
ascended upward. Holtz discovered that the pods of ore were replacements of sandstone
which developed on the underside of the sheets, perhaps accounting for their random
placement. Some ore pods were close to the surface (thus accounting for Mumper's surficial
discovery), and some were deeper along the underside of the sheets. Although limestone
occurs in the immediate vicinity, Holtz determined that the replacement occurred in the
sandstones of the area. This may account for the fact that Dillsburg never produced the
broad mineral assemblage seen at Cornwall and French Creek.
The Dillsburg orefield, perhaps because of its random nature and lack of large mine
dumps, has not been an area of great interest to mineral collectors. It takes a dedicated
effort (usually in the winter) to locate the mine areas and scope the terrain just to get
a grasp of the earlier layout. In the 1970's, the area was studied by Robert C. Smith of
the (Fourth) Pennsylvania Geological Survey. His efforts, in conjunction with the study of
local diabase, produced an interesting mineral assemblage. Smith elected to include the
locality in the most recent version of G33, the popular "Mineral Collecting in
Pennsylvania." Although most of the minerals are microscopic in nature, 19 distinct
species have been identified. Among the most interesting are small, but brilliant,
octahedral magnetite crystals, datolite in clear to pale green crystals, small white
apatite crystals, and a bright pink iron rich muscovite mica which appears as clay-like
masses.
In 1992, a group of members from the Northern York County Historical and Preservation
Society formed a committee to study and preserve all known information relating to mining
in the Dillsburg area. The efforts of this dedicated group of volunteers resulted in a
publication completed in 1995 entitled "Mines of the Dillsburg Pennsylvania
Area". This work features a large number of historical photographs never before
published. The object of the publication is to preserve a record of one Dillsburg industry
whose landmarks are rapidly eroding. Most residents of the town are not aware that mining
ever existed in the region.
Stay Tuned for Part Four:
The Lead-Zinc Mines of Sinking Valley.
