656 B. N. PEACH AND J. HOENE ON THE 



the stony clay to the finely grooved pavement of sandstone, so that 

 the glacialist can examine thoroughly the nature of the deposit. 

 It consists of tough red clay, packed with smooth and striated 

 stones scattered irregularly through the section. There is no 

 trace of stratification in the deposit, as it retains the same tumul- 

 tuous character throughout. The stones are beautifully striated 

 along the major axis, and are mainly composed of the underlying 

 red and yellow sandstones, varying in size from an inch to several 

 feet across. In addition to these wo noted smooth chalk-stones, 

 chalk-flints, and subangular blocks of the grey flagstones. The 

 most interesting feature, however, is the occurrence of small worn 

 fragments of marine shells which a,re scattered indiscriminately 

 through the deposit ; they are smoothed and striated precisely in 

 the same way as the stones in the Boulder- clay, as if they had 

 been subjected to the same abrasion. 



Shelly Boulder-clay was also observed on the west coast of Sanda, 

 between Spur Ness and Stranquoy ; and sections of the same de- 

 posit are to be found in Bacaskeal Bay. In the Burness peninsula, 

 near the Holms of Eyre, the shore is bounded by low cliffs of purple 

 shales and flags, with a coating of Boulder-clay, which is just suffi- 

 cient to cover the surface of the rocks. It is chiefly composed of 

 fragments of the underlying rocks, but likewise contains fragments 

 of sandstone, granite blocks, and smoothed stones of gneiss and 

 schist, all of which, except the sandstone, are foreign to the island. 



In Stronsa several important sections were met with both on the 

 east and west sides of the island. On the shores of Linga Sound, 

 not far from the narrow isthmus of Aith, a section of shelly Boulder- 

 clay occurs resting on grey sandstone, the deposit being upwards of 

 25 feet thick, and comprising chalk, chalk-flints, and white quartz, 

 in addition to the blocks derived from the flags and sandstones of 

 the island. Purther, on the north-east corner of Rousholm Bay a 

 thin coating of this deposit rests on the flagstones, which are bent 

 over to the north-west in the direction of the ice-flow. 



One of the best exposures of Boulder-clay in Orkney occurs on 

 the eastern shores of Odin Bay, in Stronsa, where it forms a con- 

 tinuous cliff for nearly half a mile. At intervals the section is 

 obscured by a grassy covering, but every succeeding storm washes 

 anew the face of the cliff, and exposes a fresh surface for examina- 

 tion. The deposit, which varies from 20 to 30 feet in depth, con- 

 sists of a tough gritty clay of a reddish colour, full of well-smoothed 

 and striated stones, which are mostly of small size; There are 

 few large boulders to be seen, the largest rarely exceeding a foot in 

 diameter. There is not the slightest trace of stratification from one 

 end of the section to the other, as the stones are disposed irregularly 

 through the clayey matrix. By far the greater number of the 

 included blocks have been derived from the flagstones and the sand- 

 stones which occur in the neighbourhood ; but the following rocks 

 are likewise represented : — granite, pink porphyritic felstone, gneiss, 

 schist, quartzite, white quartz, dark limestone, with abundant plant- 

 remains, which is probably of Oalciferous-Sandstone age, oolitic 



