308 REPORT— 1894. 



the sliells, which were therefore 510 feet above the level of the sea. I could 

 entertain no doubt as to the nature of the superincumbent matter, as that 

 part of it which had been thrown out was left lying at the mouth of the 

 well. It was unquestionably the true till. Indeed, if I had entertained 

 any doubt as to this point, it would have been removed by the discovery 

 of a small granite boulder, which was found about 2 feet above the bottom 

 of the till. The nearest granite rock in that direction (N.W.) is at 

 Cruachan, about sixty miles N.W. of Airdrie. . . . 



' I may add that ]\Ir. Russell states that after passing through the 

 shelly bed of brick-clay, he came again to the till, thus proving indispu- 

 tably what has always been suspected, that there has been more than one 

 deposition of the till or boulder-clay.' ' 



(ii.) Sir Archibald Geikie. — In the preparation of his valuable memoir 

 on ' The Phenomena of the Glacial Drift of Scotland,' published in ISGS,'^ 

 Sir Archibald Geikie visited the spot, also under Mr. Russell's guidance. 

 He described it as situated ' on the crest of a ridge which, rising high 

 above the surrounding country, commands an extensive view across the 

 lower part of the basin of the Clyde. On the water shed of this high- 

 lying ridge a well was sunk some years ago, and while the excavations 

 were in progress the shells were found.' Sir Archibald then gives particu- 

 lars corresponding with those stated by Mr. Smith, adding that the till 

 underneath the shelly clay was ' about 24 feet thick, and lay directly on 

 the Carboniferous strata of the district. The brick-clay at its thickest 

 part,' he continues, 'measured 2 feet 1 inch in depth, but thinned away 

 rapidly on every side, so as to allow the upper and lower till to come 

 together. From a number of additional wells, sunk on purpose, Mr. 

 Russell ascertained that the clay lay in a hollow of the undermost till, 

 and that this hollow measured about 19 feet long by about 5 feet broad. 

 Pits which were dug beyond the boundary of this little trough showed a 

 great depth of the usual till, but without a trace of brick-clay. The 

 shells consisted entirely, I believe, of Tellina proxima. Usually the 

 .specimens were broken, but a good many were taken out entire, with 

 both valves together.'* 



(iii.) Dr. Crosskey. — About the same time as Sir A. Geikie's visit,, 

 or apparently before it (though the account was later in being published), 

 Dr. Crosskey visited the locality, and made some observations which were 

 communicated in a paper to the Geological Society in January 1865.^ He 

 remarked : ' One of the most perplexing cases in Scotland, upon any theory 

 of the formation of boulder-clay, has been the alleged occurrence at 

 Chapelhall, near Airdrie, of a bed of clay containing 2'ellina calcarea, 

 intercalated between the masses of true boulder-clay. 



' The facts relating to the discovery of these shells have been recorded 

 by Mr. Smith. . . . The present paper will simply examine the question 

 whether the superincumbent matter was, without doubt, the true till.' 



After defining what he means by the term ' a compact, unstratified 

 clay, with a large proportion of striated stones, chiefly of local origin,' and 

 stating that ' the glacial shells in the west are never found within the 

 boulder-clay proper,' but ' invariably above it,' Dr. Crosskey proceeds : 



' Mr. Russell (the original discoverer of the shells) reports that the 



' 'On the Occurrence of Marine Shells in the Stratified Beds below the Till.' 

 Op.cit. pp. 1311-112. 



* Trans. (Icol. San. Glas. vol. i. part 2. ' Ihid. pp. 58-9. 



* Quar. Jour. Giol Soc. vol. xxi. 



