Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/84

56 F³. In Huntingdon county, (Rep. T³, p. 123,) Prof. White divides No. VI as follows:

1. An upper division, consisting of impure and shaly limestone and containing a 25’ massive layer with Stromatopora fossils133′.

2, A middle division, dark blue massive limestone, not fossiliferous, and containing mostly good limestone beds,90′.

3. A lower division of shaly, impure limestone170′.

The total thickness of the formation is thus about 300′, varying from that up to 400′ in other parts of the county. All the good beds, most quarried, are confined to the middle division, 90′—100′ thick.

Along the Susquehanna the series is from 250′–300′ in Union county and may be conveniently divided into—

The total thickness of the group averages about 250′ as against 350′ in Huntingdon, and 250′ in Perry. It must be remembered in comparing these sections that the “Bossardville limestone” group of the Susquehanna, corresponds to No. 5 of the Perry county section and to No. 2 of the Huntingdon county section, the lower division of the latter 170′ thick, consisting of impure limestone, and in this report considered a part of the next lower group—the Upper Salina, Vc′.

The practical point brought out by this comparison is the fact that the Lower Helderberg (Lewistown) formation in this central district furnishes a series of limestone beds, non-fossiliferous and massive, and about 100′ thick, which contains nearly all of the pure stone of the series, probably averaging 50 per cent. of the entire group thickness, and that the good burning beds are to be sought in this series