Page:Quarterly Journal of the Geological Society of London, vol. 32.djvu/292

212

inland sections, exhibiting the junction of the Triassic and Liassic beds, are rather scarce in this country. I wish, therefore, to describe an exposure of the Rhaetic beds near this town, which is of interest as proving the continuity of that formation and the remarkable persistence of lithological conditions in its strata; whilst the occurrence of some new species of fossils shows that our knowledge of the life of that period is, as yet, very incomplete.

These Rhætic beds are to be seen in three brick-pits situated at the northern extremity of the Spinney Hills, a low range forming the eastern boundary of the town of Leicester and the Soar valley (fig. 2).

The Rhætics form a capping to the hills at this northern end; but southwards, as the ridge rises, they are overlain by a thick covering of drift to the depth of at least 20 or 30 feet.

Eastwards the upper members have been denuded by a little stream, the Willow Brook, although the lowest bed (the Grey Marl) is nearly, but not quite, continuous right across to Crown Hill, where Lower Lias beds (yellow fucoidal limestones) first put in an appearance (see fig. 2).

The floor of the brick-pits just mentioned is about 10 feet deep in red Upper Keuper Marls. Descending sections in neighbouring pits and in the railway-cutting near the station show an alternation of Red, Grey, and Blue Marls to a depth of from 80 to 100 feet. It is noticeable that the relative thickness of the red bands becomes less as we approach the top. Selenitic crystals and salt pseudomorphs occur in these beds; but they have as yet exhibited no traces of life. A thick nodular band of gypsum occurs about 60 feet down.

Close to the eastern foot of the Spinney Hills a boring for coal has reached the depth of 741 feet (fig. 2). This commences just below the Rhætic Grey Marl, and passes through 690 feet of Keuper Red Marls containing much fibrous gypsum, and in the lower part thick red clays, and then enters a bed of sandstone, through which it is now passing. It would thus seem probable that these Triassic beds thicken in this direction; and as we are receding from Charnwood Forest (a Triassic island), this would be a likely consequence. Of the 51 feet of Lower Keuper Sandstone, the first 20 feet is described by Mr. J. A. Bosworth, F.G.S., the engineer, as a perfect quicksand, no solid cores being obtained. At Hinckley, twelve miles to the S.W., the Red Marls are of the same thickness, as proved by a borehole for water, of which a good supply was obtained, but too much impregnated with mineral matters for use; the same thickness of marl was also proved at Rugby, where the water was equally bad.

In the brick-pits the Rhætics are seen to rise nearly vertically for about 30 feet above the Red Marl, to which their stratification is