POST-TERTIARY FOSSILIFEROUS DEPOSITS. 83 



at different heights, exactly as in the line of hillocks now fronting the sea. Following the 

 Irvine Water, at about two miles from the sea, a section of clay and sand beds was cut 

 out by a curve of the stream. Of all sections of this character it nuist be noted that the 

 looseness of the material causes them quickly to appear and disappear, so that the 

 observations made at one season cannot often be repeated. 



The section we examined was the following : 



1. The base of the section was the Boulder Clay of the true normal type. The 

 boulders, chiefly of trap and limestone, were not very far-travelled, and were beautifully 

 . striated. As usual this Boulder Clay had sharp undulations and dipped violently within 

 short distances, rising nearly to the surface in one direction and passing down rapidly 

 beneath the stream, a variation of one to twenty feet in its height taking place within a 

 quarter of a mile. 



The Boulder Clay was capped occasionally along the line of its outcropping by a few 

 feet of ferruginous gravel. This gravel, as well as the Boulder Clay, has been greatly 

 denuded, and occurs in patches only. It may be recognised in good sections of the 

 glacial series of beds, as at Lochgilphead, where it covers the Arctic deposit, but it is not 

 at all persistently found. 



3. Here occurs a vast gap in the normal arrangement of the strata. The Boulder 

 Clay was not followed by the series of glacial fossiliferous sands and gravels of the Clyde 

 district, but was simply covered here and there by a layer of peat a few inches less or 

 more in thickness. 



4. Following the peat appeared the first great shell-bed in the section. At the 

 point described tlje Boulder Clay was hollowed out and disappeared under the 

 stream. 



The old clay had evidently been disintegrated, and its boulders rolled upon a beach. 

 The small boulders scattered about were of the same composition as those of the older 

 bed, but their striations were gone, and they had evidently been subjected to the rolling 

 action of the waves. 



Among the shells embedded in this old sea-bottom not a single purely Arctic form 

 could be detected, although it was twenty feet -beneath the surface, and rested immediately 

 on the Boulder Clay. 



The valves of the specimens were generally loose and' separate, yet several perfect 

 examples were extracted, and from the very bed of the stream a fine example of Madra 

 stuUorum was obtained in sitii, clearly proving that it was not a mere drift-bed, but that 

 many of the Mollusca lived and died upon the spot. The action of the Irvine Water, often 

 rising to great heights, would be sufficient to break up the shells and scatter them on the 

 banks. 



5. Upon this rough sea-bottom, with its stones washed out from the disintegrated 

 Boulder Clay, rests the fine sand of the district. In this sand, fourteen feet from the 

 surface, and about four feet above the average level of the stream, immediately before our 



