Here is the traditional account of the start of the slate industry in the area: "In 1844 two Welshmen, William Roberts and Nelson Labar, who were traveling in this region, became instrumental in bringing into existence a great industry and incidentally the town of which we write. While making the journey on foot from Easton to Mauch Chunk by the old stage route along the Lehigh, they discovered at one of their resting places,
opposite the site of Slatington, some pieces of stone, leaning against the barn of Peter Heimbach, in which they recognized a close resemblance to the merchantible (sic) slate of their native country." [The Slatington News, 9 January 1892, notes that this became the famed Heimbach quarry, a bit northeast of Walnutport.]
Tunnel quarry opening in 2014; photo credit Richard Musselman
A short time later, Owen Jones and William Roberts, leased land from Jonas Kern, and opened a quarry in the hill on the east side of what later became known as the Welshtown road. This was the first slate operation in Slatington, and the "tunnel quarry" operated until about 1886. [The Slatington News, 9 January 1892, published some of the terms of the original lease. See also the account of D.D. Jones in The Slatington News, 19 July 1876.]
In the decades that followed, quarries opened and closed all around Slatington. [The Slatington News, 9 January 1892: the Washington quarry in 1848 at the northwestern limit of the town on Trout Creek and the Douglass quarry in 1849 at the foot of Second Street; The Slatington News, 19 July 1876: 1846 Douglass quarry near J.D. Ermack's factory, The Mantel Quarry (Lehigh Slate Co.) in 1847, Washington Quarry and Williamstown Quarry in 1848, first school slate factory on the north branch of Trout Creek in 1849.]
Slate was needed for roofing, school slates, blackboards, mantels, and a lot of other architectural and building uses. By 1914, the immediate Slatington area had over twenty active quarries, employing upwards of a thousand men, and there were also accompanying slate factories.
Immigrants came to the area to work in the quarries, and many of those immigrants were from Wales (see the chart on the percentage of the town's population from Wales). The town's population rapidly increased in the late 1800s.
Tunnel quarry historical marker in 2014; photo credit Richard Musselman
Sources: Pictorial Souvenir Scenes of Slatington and Vicinity; History of the Counties of Lehigh and Carbon in the Commonwealth of Pennsylvania (1884); The History of Lehigh County (1914)