ON THE SHELL-BEARING DEPOSITS AT CLAVA, AND OTHER PLACES. 485 



the work proceeded it had to be made longer and wider, owing to slips of 

 clay and saud from the face of the cliff. Though the work was seriously 

 impeded by unfavourable weather, the excavation was eventually sue- 

 cessful in showing an admirable section of the shelly clay and underlying 

 gravel, without reaching the solid rock. 



The section thus revealed by the exposed surface of the cliff and the 

 trench was as follows : — 



Feet 



1. Surface soil and boulder clay from top of ridge of drift 



= 43 feet, of which only the lower 12 feet exposed to 

 view (see Section of ' Main Pit,' p. 15) . . . .12 



2. Fine sand 20 



3. Blue shelly clay 16 



4. Coarse yellowish-brown gravel 10 



Throughout this report this excavation is referred to as the ' main pit * 

 or ' main section ' of shelly clay. 



A careful examination of these various deposits was made on the 

 ground by most of the members of Committee, with the following 

 results : — 



1. Boulder Clay, overlying the sand and shelly clay. — As this deposit is 

 ■extensively developed in the neighbourhood of Clava, the Committee 

 selected a typical section for examination, where there is a splendid 

 exposure of the included blocks. The section occurs on the south bank 

 of the Cassie Burn, from 130 to 160 yards south-west of the ' main pit,' 

 where the boulder clay also overlies the shelly clay, and where the deposit 

 resembles in every particular that above the ' main pit.' 



The deposit is of a light brown colour, and the matrix consists mainly 

 •of fine sand ; the stones are more or less well-rounded, varying in size 

 from fine gravel up to 2 feet in diameter. Many of the blocks of 

 sandstone are finely striated along the longer axis. The deposit is more 

 sandy and gravelly than the typical ground moraine or till of Scotland. 

 But though the proportion of clay among the materials is small, it is 

 usually sufficient to bind them into a compact mass. 



The largest proportion of the included blocks has been derived from 

 the adjacent Lower Old Red Sandstone strata. Of these many have 

 "been obtained from the micaceous flagstones occurring m situ, in the 

 Easter Daltullich Burn, the river Nairn, and other localities to the west 

 and south-west of Clava. On referring to the table of percentages of 

 stones, which has been prepared to show the variation in the character 

 of the included blocks in the shelly clay and associated deposits, it will 

 be seen that while the percentage of Old Red Sandstone blocks in the 

 overlying boulder clay varies from 56 to 76 per cent., in the shelly clay it 

 amounts to only 17 per cent. No organic remains have been found in this 

 deposit, 



2. Fine Sand. — The sand underlying the boulder clay in the 'main 

 pit ' is of a yellowish brown colour and fine-grained. At first sight it 

 seems to be free from stones, but on closer examination a few may be 

 detected under a quarter of an inch in size. The lowest 4 feet of sand 

 overlying the shelly clay is very compact, harder even than the latter 

 deposit. The line df junction between the sand and shelly clay is nearly 

 horizontal, and clearly defined by a difference in the colour and texture of 

 the materials. The boundary line between the sand and overlying boulder 

 clay is less distinct. After a heavy rainfall or the frosts of winter, lines 



