of Mr. Sanders he saw good reasons for changing, at one or two points, the numbering of the series. Some of the beds which Mr. Sanders distinguished apart, were considered by Mr. Hartshorne to be solid beds, and vice versa. The number of Mr. Sanders beds, (ninety-eight) was, on the whole, increased to one hundred and fifteen, leaving the sequence, however, unchanged.

Mr. Hartshorne being called away to take an important position in the Bessemer iron manufacture, the continuation of the work was intrusted to Mr. S. S. Hartranft, a graduate of Lafayette college, under the direction of M. A. S. McCreath, the chemist of the survey in the laboratory at Harrisburg. Mr. Hartranft completed analyses of beds No. 93 to No. 115, the last visible in the exposure, as numbered by Mr. Hartshorne.

The following is a tabulated statement of the general result.*

To show the extent of the investigation and the thickness of the whole exposed mass, as well as the relative thickness of each of its layers, I will give, first, Mr. Sanders' original series of numbers, thicknesses, and lithological descriptions, as follows:

* Brought up to date of publication of this lecture, October, 1878.

This last and lowest bed visible at the north end of the exposure is calculated by Mr. Sanders to lie 1280 feet above the lowest bed of the whole series of Cambro-silurian limestones in our State. This calculation is made by projecting curves according to all the observed dips, between the north end of exposure and the edge of the slate county to the north, checked by dips in a series of exposures on the east bank of the river. It is not necessary to go here into a discussion of the existence of a great upthrow fault between the limestones and slates.

The topmost bed No. 1 of the series is therefore 1280'+426′=1706′ above the Formation No. I.

The upper limit of the limestones, where they pass conformably beneath the Utica or Hudson River slates, is seen several miles down the river. By projecting dip-curves in the interval Mr. Sanders measures an additional thickness of limestones amounting to 1819 feet.

The total observed thickness of the great limestone formation (No. II of the old Pennsylvania survey, including representatives of Calciferous, Chazy, Birds' eye, Black-river, and Trenton limestones) is 3535 feet.

The beds selected for examinaaion lie therefore a little below the middle horizon of the mass, and undoubtedly belong to the "Calciferous Limestone Formation" of the New York geologists, the Magnesian Limestone Formation of the western geologists.

I will now give Mr. Hartshorne's re-numbering of the beds, with his and Mr. Hartranft's determinations of their chemical characters, but omitting their lithological descriptions. The recorded analyses are to the third decimal place; but in the following table only one (and the nearest) decimal is given, as this will not affect the law, and will assist the eye:

Without discussing in detail, at present, this instructive table, several things are evident at a glance, viz: that

1. Alternate strata of limestone and dolomite make up the mass. 2. The dolomite layers carry the most insoluble materials, as a rule. 3. Specimens taken from the top and bottom of the cut (thirty feet apart, or less) differ sometimes as notably from one another as specimens taken from different beds; but, as a rule, each layer is nearly homogenous, so far as two or three analyses can show such a rule.

4. Not one of all the so-called dolomite layers has enough carbonate of