Letter of Mr. D’Invilliers.
711 Walnut Street,
Prof. J. P. Lesley, State Geologist:
Dear Sir: I have the honor to transmit herewith my report upon the geology of Union, Snyder, Mifflin and Juniata counties, the field work of which was largely carried on during the season of 1888, The high state of cultivation effected through this district between the Susquehanna and Juniata rivers, and its ready accessibility, except in the region of the Seven mountains along the Center county line, made an exploration of its area comparatively easy, while the effective, and in many cases detailed examinations of the field carried on at different times by my predecessors on the First and Second Geological Surveys, had already put on record such a general delineation of its structure and geology as to make extensive repetition of these facts unnecessary.
As the commercial features of the district are confined almost solely to the fossil (Clinton) ore-beds of No. V, the Lower Helderberg limestone of No. VI, and (in the western part of the district) the glass-sand of the Oriskany sandstone formation No. VII, considerable time and attention was given to tracing the outcrops of these three rock-groups; an examination of mines and quarries; and, as far as possible, a correct delineation of their outcrops on the maps. It was hoped that a very complete record of the various ore-mines and the characteristics of the several ore-beds of the Clinton formation might be obtained; but the utter prostration of the iron industry through the Juniata
