672 MR DAVID MILNE HOME ON THE BOULDER-CLAY OF EUROPE. 



dence superfluous. It therefore may simply be mentioned, that confirmatory 

 evidence is afforded by numerous cases of boulder-clay alternating with strata, 

 the marine character of which is indisputable. Localities are mentioned by Mr 

 Geikie* as occurring in Roxburghshire, Lanarkshire, and Ayrshire, where beds 

 of unstratified boulder-clay, 30 to 40 feet thick, alternate with beds about the 

 same thickness of stratified clay and stratified sand, the former sometimes con- 

 taining marine shells. In such cases, the boulder-clay virtually forms part of 

 the series. 



5. Several observers, who have found marine shells in the boulder-clay, have 

 been struck with their broken or fragmentary condition. This feature is not 

 observable in the stratified or laminated clay beds where the same shells occur. 

 In the brick clays of Lanark, Renfrew, and Ayr shires they are found perfect in 

 form, and apparently in their natural position. But in boulder-clay, the same 

 shells have been mutilated and smashed, so that it is difficult to identify the 

 species, -j- Is it not a fair inference from this fact, that the beds in which, at the 

 bottom of the sea, these shells had lived, must have been disturbed and deranged 

 by some intrusive body of great weight and power, which both crushed the shells 

 and obliterated all traces of stratification or lamination in the structure of the 

 beds ? It seems to me that such effects would result from the intrusion of ice- 



* Glacial Drift, pp. 54 to 65. 



•j- Thus Dr Watson, in describing the boulder-clay of Arran, says that the shells in it " are 

 very much broken. The shells may often be found crushed, yet with each fragment in its own place. 

 Some of the large specimens of Cyprina, though unbroken, are indented, as by a sudden violent 

 blow. The whole condition of the shells suggests that heavy stones have been dashed down upon 

 them." Dr Bryce also notices that the Arctic shells found by him in Arran were " in single valves 

 or in a fragmentary state, yet not so small but that the species can be determined." — Geology of 

 Arran, p. 168. 



The shells in the boulder-clay of Caithness have been examined by a great number of com- 

 petent geologists, who all give the same testimony. Mr Peach describes the shells so " broken" 

 and "rubbed" he could find only one entire shell. Messrs Crosskey and Robertson of Glasgow, 

 having gone to Caithness on purpose to examine the boulder-clay there, describe it as " a hard and 

 compact mass, with striated and polished boulders, being in appearance similar to that in the west 

 of Scotland. The shells are thinly interspersed from top to bottom, and are of a water-worn and 

 fragmentary character. They appear equally distributed, as if the whole mass had been mixed up 

 and kneaded together." — Geolog. Society of Glasgow Trans, vol. iii. p. 126. Mr Jameson of Ellon 

 says that the drift-beds of Caithness contain " remains of sea-shells all through them, and these are 

 broken, rubbed, and scratched, and evidently by the same agency that marked the rocks and 

 boulders." His theory to account for the facts, is, that " much floating ice seems to have passed 

 over the district from the N.W., which crushed and destroyed these marine beds, broke the shells, 

 and mixed them up with other superficial debris into that mass of rough pebbly mud which now 

 overspreads the surface." — Proceed, of Lond. Geol. Society for 1865, pp. 176-7. 



Mr Jameson has also the following statement regarding a deposit of boulder-clay near Paisley 

 which he examined. He says — " I sometimes found, on heaving up a boulder, a number of young 

 crushed mussel-shells beneath it, as if they had been squashed by the fall of the stone. The clay 

 around also occasionally exhibited black stains, as if from the decay of sea-weed that had been attached 

 to the stone." 



At the various places where the Rev. Mr Crosskey found sea-shells in boulder-clay, along the 

 coasts of Scotland, England, and Ireland, the shells were ' very fragmentary, and even single valves 

 are seldom found whole." — Glasg. Geol. Soc. Trans, vol. iii. p. 151. 



