Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/70

42 F³. and character of the Palaeozoic rock-column in the Juniata district.

It must be remembered however that there is no sharp line or plane of division between the various groups, the one imperceptibly grading into another, and their planes of contact often concealed by débris, so that the thickness assigned to the successive groups are only approximately and relatively correct.

And it can never be otherwise, from the very nature of their deposition. The constant thickening and thinning of the various rock groups make it impossible to fix absolute measurements, so that too great stress must not be put upon the figures subtended below.

Two complete vertical sections are given to explain the map coloring and give an idea of the approximate thickness of the different rockgroups:

(A) Section of Mifflin and Juniata county, mainly from reports F and F² and from personal surveys.

(B) Section of Union and Snyder counties from reports G⁷, T⁴ and from personal surveys.