Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/15

Rh at Logan gap, McVeytown, Mt. Union, etc. there exhibited, constructed by our lamented Charles A. Ashburner, then aid to Mr. Dewees, are of unsurpassed excellence. That report covered part of Snyder county, and carried the geology of the district far across Huntingdon county.

Unfortunately the curious and beautiful map of the contour line survey of the south flank of Jack’s mountain from Logan gap to Jack’s narrows made in 1875 by Ashburner and Billin has never been published.

But a more important contribution to the geology of the district was Mr. C. E. Billin’s contour-line survey map of the Seven mountains made in 1876–77, published partially in Grand Atlas, division V, part 1, and now in a separate atlas. Besides the map itself, more than a dozen elaborately constructed cross-sections show the structure of this mountain mass, the western spurs of which project into Huntingdon and Mifflin, and the eastern spur sink into the red shale plain of Union and Snyder. A special map of the Greenwood furnace or great Stone mountain fault and another of the zigzag outcrop lines of the fossil ore beds in western Huntingdon county are included in the set of sheets.

Mr. d’Invilliers’ field and office work extended over more than a year, and no part of the four counties was slighted. The completeness of his report is as remarkable as its accuracy in detail. It brings down the history of the iron industry of the district almost to date, showing its decline and the cause of it, without reference, however, to the great fact that the concentration of iron-make at great centers of production, the large introduction of northern, western and foreign richer ores, and especially the substitution of Bessemer for cast-iron pig, have combined to change the status of the old iron-ore-producing districts of Pennsylvania.

Readers will notice that Palæontology is excluded from this report. No collections of fossils were made. The reader is therefore referred to Prof. Claypole’s and Prof. White's reports on Perry, Huntingdon and NorthumberandNorthumberland [sic] counties, and to my Dictionary of the Fossils of