1869.] GEOLOGY AND MINERALOGY. 353 



(2) The included stones have very feeble polish, and only faint 

 reminiscences survive of their former striations. They have 

 evidently been much worn in many cases, and in others have not 

 been subjected to any extreme glaciating force. (3) It is not 

 fossiliferous. 



The older boulder clay, and this younger boulder clay may 

 sometimes be seen resting upon each other. At Chapel Hall, 

 Airdrie, a good example of this occurs. The line of separation 

 in a well dug by Mr. Russell in his garden, might even be detected 

 by the eye, and it was in a deposit occurring between the two 

 that fossils were found. 



Sometimes a shell bed may been seen in sections intervening 

 between the older and the newer boulder clay. This may be 

 admirably studied in the beds before alluded to near Lag, Arran.* 



In regular and ascending order may be seen the older boulder 

 clay — 1 of this paper; unfossiliferous and typical. 



The fossiliferous clay — 3 of this paper ; with a scattering of 

 striated stones; a wash from an older bed, indicating depression. 



Younger boulder clay — 4 of this paper ; unfossiliferous, loose 

 and sandy, with feebly striated stones ; the most recent bed which 

 can be attributed to ice action. 



If there be any truth whatever in these divisions of " boulder 

 clay," it is evident that to speak of a fossil as found in boulder 

 clay, or under boulder clay, is a most vague and indefinite phrase. 



A shell may be said to occur in the boulder clay, and may 

 have been found in the second, third, or fourth, of the beds 

 discriminated in this paper ; or a shell may be said to occur under 

 the boulder clay, and may have been found under the first or the 

 fourth. 



A fossil really belonging to the age of the Paisley clay may 

 thus be ascribed to a more remote or a more recent era, to the 

 great confusion of any attempt to understand either variations of 

 climate or distribution of species during the glacial epoch. 



The classification of boulder clays in this paper is given as a 

 suggestion rather than in any way as an established arrangement, 

 with the view of urging upon the members of the Society the 

 necessity for more extended investigations. 



* See a joint .account of these beds by E>r. Bryce and the writer, 

 ' Geology of Arran." — P. 166, 2nd edition. 



