DEPOSITS AND ELEVATION. 21 



are not infrequent. They occur in the edges of tables of 

 rock still in situ or broken off and lying in the sward. 



7. On the second or third reef (marked by a loose 

 spherical boulder at its eastern and higher extremity), a 

 fallen slab of very hard stone showed in its underside 27 

 holes, all of the narrower form, and one 2" deep"^. Height 

 570 feet. 



8 and 9. The next reef yielded good specimens at 540 

 feet; and the one below, others at 520 feet. 



Leaving the eastern precipices of these reefs by a path 

 which skirts a long, enclosed field on the north side, and 

 leads to the mining-works, one passes a great egg-shaped 

 boulder 6 or 7 feet long, lying on the sward. This, with 

 the true Pholas-holes, exhibits also, from its exposure, 

 many of the tubular and semitubular corrosions which 

 might easily be mistaken for the remains of burrows. It 

 shows also a very perfect polishing of parts of its surface, 

 which I have heard described as glacial, but which, in truth, 

 is only the effect of the secular attrition of Ovis aries. 



10. As a further illustration of the distribution of these 

 PAo/«5-burrows, I may mention that they occur in consider- 

 able abundance and remarkable preservation in various parts, 

 and especially in the topmost plateau, of the Little Orme^s 

 Head. This flat looks sea-worn, as if, except for lichenous 

 growths, but yesterday tide-washed ; and I do not exag- 

 gerate when I say that on that ancient scar I seldom failed 

 to find the holes, on examining any piece of rock which 

 seemed to me such as, on a modern beach, would have 

 afforded suitable habitat for the mollusk. I exhibit two 

 very characteristic groups of six and nine holes respec- 

 tively*. One splendid specimen with seven holes, each 

 more than 2 inches deep, was unfortunately destroyed in 

 the process of quarrying it out. 



In the preservation of these burrow^s in loose beach- 

 stones, and in the edges of the tables of outcropping strata, 



