On 25 September 1907 the Robert and Isabella's children registered themselves as directors of the “Robert L. Jones Slate Manufacturing Company”. Retrospective newspaper reports confirm this:
The charter for the Robert L. Jones Slate Manufacturing Company, capitalized at $50,000, was received September 25. The directors of the company were, Emma E. Smith, J. Hayden Jones, Isabella Jones, Peach Bottom Township; E. W. Keyser, Bridgeton; Arthur L. Jones, Delta. Federal engineers were surveying portions of York and Lancaster Counties, preparatory to making a topographical and geographical map of the triangle, including the location of mines, minerals, elevation and watersheds.[Delta Herald-Times, 6 Oct. 1932, p 2 (see here)]
The Gazette and Daily (of York, Pa), 26 Sept 1957, p 18 added that registration had taken place at York. The directors were the five children of Robert and Isabella, together with E. Winchester Keyser who was cashier of the First National Bank of Delta, of which Robert had been president.
"Stone; an Illustrated Magazine, XXVIII, June, 1907, - May, 1908 carried an ad and an article containing much the same information:
Estate of R. L. Jones
The Estate of R. L. Jones is continuing the business established by the late Mr. Jones of manufacturing Peach Bottom roofing slate at Delta, Pa. The Jones quarry is the one long known as the "Old Big Quarry," located in Peach Bottom Township, York County. It was opened about the year 1800, and was for many years operated by Rowland Parry; afterwards by Isaac Parker & Co. Slates from this quarry obtained the first premium at the Crystal Palace Exposition in London in 1850. Its product established, it has since maintained the very high reputation of the Peach Bottom slate. Roofs in the vicinity covered with the first slate taken from this quarry remain as perfect in all respects as when first laid on. The material is strong and imperishable, and the color is uniform and unchangeable. [ Page 238]