ISLA. ALLUVIA. 237 



but they are most conspicuous on the shores of Loch in 

 daal, which they skirt for a very considerable space. 

 Having here been in former times exposed to the imme- 

 diate efforts of the sea, they are abruptly cut down, so as 

 to form a series of high banks, attaining, in some places, 

 even sixty feet in height. The effects of this waste, and 

 of other gradual accumulations of gravel and sand, have 

 been such as by degrees to exclude the sea from further 

 access to them ; producing the spits of sand which render 

 the entrance to the anchorage of Loch in daal so narrow, 

 and shoaling the water all along the upper parts of the 

 bay so as to have admitted of an obvious encroachment 

 of the land upon the sea. These beds are popularly 

 imagined to have been thrown up by the sea, and to be 

 the remains of ancient beaches ; but to disprove this 

 opinion it is sufficient to state, that the alluvia, although 

 consisting in part of rounded gravel, contain perhaps an 

 equal portion either of clay or of vegetable mould mixed 

 throughout their whole mass. They are obviously therefore 

 derived from other causes. Their superficial extent, as 

 well as depth, prevents the possibility of their having been 

 formed by any rivers which could have had their rise in 

 Isla ; and we must therefore rest in the general conclusion 

 that they appertain to some unknown period, and to some 

 diluvian action, similar effects of which are to be observed 

 in every part of the globe. It is more remarkable that 

 they should be so generally wanting throughout the 

 Western islands, than that they should be so conspicuous 

 in Isla. But I must observe that, at whatever time they 

 have been deposited, their origin does not appear to be 

 very remote in respect to distance of place ; since the 

 pebbles are almost entirely formed of quartz rock, similar 

 to that which constitutes both Jura and the high ridges 

 of this island. Besides these alluvia, there are circum- 

 stances visible between Loch Gruinart and Loch in daal, 

 which mark the recess of the sea; but whether at this 



