Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/529

1870.] SHARP — NORTHAMPTONSHIRE OOLITES. 363 ft. in.

3. A bed of a peculiar character, consisting of alternate layers of calcareous and arenaceous material, each about half an inch in thickness, the former standing out in ridges when weathered. These layers are sometimes horizonal, and sometimes much and variously inclined from false bedding 3 0 4. Hard, irregular, finely laminated, shelly zone, with much carbonate of lime — contains Acrosalenia Lycettii and many oysters and other shells. This zone is not constant 0 9

5. Thinly laminated bed of alternate layers (as bed 3), but the false-bedding much more marked, sometimes inclined from right to left, and sometimes from left to right, in alternate zones 2 0

6. Similar bed, not so finely laminated, and with false-bedding, uniform in direction and less marked. Some fossils 3 0

7. Hard arenaceous limestone, in two beds, false-bedded, and becoming slaty towards the bottom 5 ft. to 6 0

One noticeable peculiarity in this section is the prevalence of false-bedding, inclining frequently in opposite directions in alternate bands, indicative of strong and diverse aqueous currents during the process of deposition. Another is the perfect manner in which the tests of shells have been preserved in the sandy zones. This I have found to be the case elsewhere, and indeed generally, in such zones.

Prominently noticeable also is the presence of several vertical pipes, of from a few inches to nearly 3 feet in diameter, which have penetrated through the whole of the calcareous beds — doubtless the effect of the dissolving action of water charged with carbonic acid. These are to be seen in section on the face of the pit : they have been filled, partly with the arenaceous residuum of the rock, partly with the sand of bed no. 2, and partly with material brought down by percolation from above.

It is curious that in every case these pipes are bridged over by the layers of the ferruginous bed at the top of the section ; upon the non-calcareous material of which, in its passage through it, the water charged with carbonic acid has had no solvent effect.

Another section of this division of the Northampton Sand is exposed in a pit near Boughton (marked h), at a distance of a mile and a half N.N.E. from this Nursery pit, and on the other side of the high ground in which are the pits first described. Here the section, about 20 feet in thickness, consists wholly of calcareous rock, divided into some half-dozen beds, containing few fossils, but showing false-bedding near the bottom.

The calcareous condition of these beds is persistent over a considerable area lying in this direction ; and they are largely quarried for building-stone, which is very durable and of a good colour. A few hundred yards south-west of the Nursery pit, is the Kingsthorpe brick-pit (i). Here is seen the base of the Northampton Sand immediately overlying the Upper Lias Clay. It presents a section of from 6 to 8 feet of the Northampton Sand, and supplies a continuation downwards of the section of the Nursery pit.

Under a bed of about two feet of weathered rubbly brown sandstone is a soft arenaceous bed (also about 2 feet thick) contain-

2 c 2