366 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 9,
So variable are the D beds here, that the excavation of a few
yards will entirely alter the details of the section. Limestone will
be replaced by sand, sand by ironstone, and either by limestone
again, with every conceivable variation of change. A limestone
band, however, about midway of the section, seems to be pretty constant
— a circumstance frequently observable in other sections of this
series, whether the beds above or below be calcareous or not.
With regard to the underlying series, E, I have observed much variation in thickness according to locality, but that, where any considerable development of thickness occurs, a greater uniformity of character is exhibited than in the D beds. I would note also, although the presence of iron in such proportion as to constitute iron-ore is generally the prominent feature of the beds E, that it is not uniformly so. Over a considerable area north of Northampton, the calcareous predominates over the ferruginous character of these beds. On the other hand, in some few localities, certain of the beds of D contain iron in sufficient quantity, probably, to render them available for smelting-purposes.
The following is the section of the pit at one point ; and although it will not tally with the section at a few yards' distance, it will serve to give a general idea of one phase of the D and E series of beds.
Section of Mr. Bass's Pit.
ft. in. ft. in.
1. Very ferruginous sandstone, in thin layers 4 0
2. Soft ferruginous sandstone, in two beds, sometimes extracted in large blocks 4 0
3. Orange sand with rounded limestone masses 3 0
4. Flaky hard ironstone with ochreous cores 1 0 to 1 6
5. Coarse sand with thin layers of sandstone, rounded at the edges, with numerous fragments of shells, joints of Pentacrinus, &c. 1 0 to 2 0
6. Calcareous flaggy bed, blue-hearted, sometimes crystalline and very hard, containing Rhynchonella cynocephala (?) and numerous R. variabilis, and much wood a few inches to 1 6
7. Red arenaceous stone 3 0
8. Ironstone in irregular beds, having a cellular texture with ochreous cores, varying in richness, and containing numerous shells in places 6 0 to 7 0
9. Limestone bed, with green centres, sometimes hard, and containing wood 1 0
10. An ironstone bed, with green argillaceous cores, full of rounded pebbles or concretionary nodules : this bed answers to the bottom bed of the Northampton Sand in the Kingsthorpe brick-pit i.
It contains Ammonites bifrons 1 0
In this section, the points of interest are — the zone, no. 6, which contains more than one species of Rhynchonella, including variabilis and, I believe, cynocephala, and the lowest bed, no. 10, in which, not unfrequently, is found Ammonites bifrons. Mr. Judd has collected from a calcareous bed, 3 feet thick, immediately overlying the Upper Lias at Brixworth (probably answering to bed no. 9 in this section), a decisive example of Rhynchonella cynocephala.
The occurrence of these distinctive forms has induced me to include this Rhynchonella bed (no. 6) and all below it in my division E
