1865.] JAMIESON LAST CHANGES IN SCOTLAND. 175 



while only twenty are known to occur to the south of this country. 

 This shows very clearly how northern is the character of the group. 

 Another circumstance of interest is the large proportion of them, 

 namely forty-nine, that occur on the east coast of North America, 

 considerably more than what now live on our own shores*. 



The proportions in 100 would be as follows : — 



Living in the seas of Britain 59 



Living to the south of Britain 37 



Living within the Arctic Circle 100 



Living on the east coast of North America .... 91 



This might lead us to speculate on some connexion between the coasts 

 of northern Europe and America during the glacial period. A 

 column is added, headed North Pacific, to show the proportion 

 occurring on the west coast of North America. I am afraid, how- 

 ever, that our knowledge of the Mollusc a of that region is as yet too 

 imperfect to warrant us in placing much confidence in the figures. 

 It would seem, from the elaborate report drawn up by Mr. P. P. Car- 

 penter, that several forms occur there which may be said to be repre- 

 sentative of those found in the North Atlantic, being extremely 

 like, although not altogether identical. If these had been included, 

 the proportion would have been much larger, 



c. Boulders of the Brick-clay — Floating ice. — Many of the beds of 

 finely laminated marine clay of this period contain few or no 

 boulders; but this is not always the case. Thus in the clay at 

 Errol in Perthshire, which contains remains of Arctic shells, I ob- 

 served that small stones are by no means uncommon, and many of 

 them are glacially scratched. Occasionally one may be found with 

 barnacles (Balani) on it. 



s. Fig. 5, — Section at Errol. N. 



1. Sandstone-rock. 3. Fine clay with Arctic shells. 



2. Boulder-earth. 4. Carse, or old estuarine mud of the Tay. 



In the Paisley brick-clay, which abounds in shells (see Appendix, 

 No. 2), boulders of from 1 to 3 feet in length are not uncommon, and 

 in the bottom of one pit I saw a block 6 feet in length. They are 

 chiefly fragments of the older crystalline rocks, and many of them 

 show the glacial striae. These boulders occur imbedded here and 



* This group probably belongs to an earlier stage of the submergence than 

 those got from most of the clay-beds of the west of Scotland, and is of a more 

 decidedly Arctic character. This is indicated by the prevalence of Leda Arctica 

 and Astarte borealis, the rather larger average size of the Tellina calcarea, and 

 the presence of some very Arctic forms, not yet reported from the western 

 beds, such as Cardium Groenlandioum, Pecten Groenlandicus, Leda lucida, 

 Leda limatula, Thracia myopsis, Mesalia erosa, M. reticulata, Modlolaria 

 Imvigata, Axinus Sarsii, and CreneUafaha. 



VOL. XXI. PAET I. O 



