A HISTORY OF RUTLAND Glacial deposits were spread out like a mantle, though the covering was doubtless of varying thickness, being thin on the steeper slopes and thick on the lower plains and in the valleys, which latter were often com- pletely filled up by the mass of debris which was driven into them by the ice. The Glacial "deposits vary also in composition and include stony clays, gravels (coarse and fine), loam and sand. In Rutland Boulder-Clay is the prevalent deposit, the patches of gravel and sand being few and small. Boulder-Clay. — This material, where it is thick and unweathered, consists of a stiff clay usually bluish or grey in colour, and crowded with fragments of many kinds of rocks which are of all sizes from a small stone to a boulder as big as a cottage. Sometimes even masses of CO to 200 yards in length are found. Many of these rock-fragments exhibit the bevelled, smoothed and striated surfaces which are character- istic of ice-borne stones. In the western and central parts of the county most of the stones and boulders are of local origin derived from the Lias Marlstone, the Northampton Ironstone and the Lincolnshire Limestone, but on the eastern side of the county and in the adjoining parts of North- ampton and Lincoln chalk and flint are the most abundant materials in the Boulder-Clay ; occasionally indeed chalk enters so largely into the composition of the clay itself that it becomes a whitish marl, and even the plants growing on its surface are species which flourish best on chalky soils. The other rocks which occur in the clay come chiefly from the Carboniferous system such as Coal Measure sandstone. Millstone Grit, and Carboniferous Limestone, but there are also occasional pieces of slate, quartzite, granite and basic igneous rocks. It is evident that the ice which accumulated such a collection of stones was not a glacier of the ordinary kind, coming from a single basin of drainage, but was either a wide spread sheet of ice or por- tions of several such sheets detached and driven by winds and currents on to a sinking land. The chalk and flint probably came from the Wolds of Lincolnshire and Yorkshire, the Carboniferous rocks came from the Pennine Hills and their borders,' and within the district itself the boulders of Jurassic rocks seem to have travelled from west to east. Of the larger transported masses, those of Marlstone, of Lincoln- shire Limestone and of Chalk are the most noteworthy. Professor Judd observes ' that masses of the Marlstone Rock-bed have been carried over deep valleys and in some cases for a distance of about 30 miles. By the detrition of the surrounding clay these huge boulders of Marlstone and Limestone often form bosses which rise above the adjacent land, and some are so large that stone-pits have been opened in them. A few equally large masses of Chalk have been noticed, one such occurring near Rid- ' It has been suggested however that the fragments of Palaeozoic and igneous rocks were derived from an older Boulder Clay, and it is believed that remnants of these more ancient glacial deposits occur near Leicester (see 'The Geology of the County near Leicester,' Mem. Geo/. Survey, 1903, p. 48).
- ' Geology of Rutland,' Mem. Geo/. Survey, p. 247.
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