TOMBSTONE CORROSION AND THE PEPPERED MOTH: QUANTIFYING HISTORICAL ACID DEPOSITION RATES IN CENTRAL ENGLAND'S BLACK COUNTRY

Ironbridge in Shropshire, located a short distance west of Birmingham, England, was the birthplace of the industrial Revolution. Although the onset of the industrial revolution changed the face of civilization, there was a price to be paid in the form of acid rain and soot from the burning of high sulfur coal. To assess the increase in weathering rates as a result of acid rain, monument corrosion data from 94 tombstones in 13 cemeteries in and around Birmingham, England, are used to establish natural weathering rates and accelerated weathering associated with acid precipitation. At each site, tombstones made from the Jurassic Portland oolitic limestone were identified. This dense limestone is well suited for the flush-lead-lettering technique. Lettering is accomplished by first carving recessed lettering into the stone. Holes are then drilled into the base of each carved letter, and a thin lead bar laid over the carving and the soft lead is hammered into the recessed letter. A broad-headed sharp chisel is used to trim the lead flush with the polished stone surface. Weathering of the limestone leaves the lettering raised above the surface. The height of the lead letters above the stone surface was measured with a digital micrometer. Ten measurements were made on the dated lined on each inscription. The high and low measurements were discarded and the average of the remaining eight measurements was determined. The highest rates of corrosion were found in the Birmingham city center and averaged 0.03 mm/yr. Corrosion rates dropped off rapidly to the southwest (the direction of the prevailing winds) but remained high to the northeast of the city. The lowest calculated corrosion rates of 0.001 mm/yr were from a cemetery in the town of Tewkesbury located fifty-five kilometers southwest of Birmingham. Corrosion rates were then converted to acid deposition rates. The spatial variation of the corrosion data were then compared to the distribution and abundance of the melanic variety of the peppered moth. Both monument corrosion data and the distribution of the peppered moth compare favorably.