James, Geikie — On Changes of Climate. 61 



is not redder than the purple rocks in the hill above, from which it has 

 apparently descended. It is arranged over the mass in horizontal 

 layers : it is clearly of subsequent and drifted origin. The Eoman 

 works which are brought into daylight by the open cutting are 

 exceedingly curious in their character and condition as mining opera- 

 tions. I subjoin a rough sketch of the mass and its overburden at 

 the B nitron mine. 



For further notice of these deposits, I beg to refer the reader to 

 Mr. A, H. Green's paper in the Quarterly Journal of Science, 1868, 

 vol. v., p. 468, and the authorities there quoted, especially Mr. J. L. 

 Thomas's admirable pamphlet on the mines of Eio Tinto, London, 

 1865. 



III. — On Changes of Climate during the Glacial Epoch. 



By James Geikie, F.R.S.E., 

 District Surveyor of the Geological Survey of Scotland. 



Third Paper. 



{Continued from the January Numher,p. 31.) 



IN my first paper ^ I gave the sequence of the Scottish Drift 

 under three groups; but in order to compare these dejDosits 

 more satisfactorily with the drifts of other countries, it is necessary 

 to subdivide them more closely. Briefly tabulated, the order of 

 succession of the Scottish Drifts, beginning with the oldest, is as 

 follows : 



Scottish Glacial Deposits. 

 ~) Intense glacial conditions (general ice-sheet), ■with in- 



1. Till with intercalated and | tervening periods marked by milder climates. The 



subjacent deposits ; )> Boulder-earth and clay being partly of land-ice and 

 Boulder-earth and clay ] partly of marine formation, indicates the decrease 

 J of the ice-sheets in the later cold periods. 



2. Moraine rubbish Retreat of great glaciers. 



3. Karnes of sand and gravel Little or no floating ice ; period of subsidence. 



4.- Brick clays, etc., with arc- ] Advance of glaciers ; period of floating-ice ; climate 

 tic and boreal shells;) not so intensely cold as during accumulation of Till; 

 Erratics j re-elevation of the land. 



5. Valley moraines.., Final retreat of the glaciers. 



Before proceeding to compare this sequence with that of Scan- 

 dinavia and Northern Europe generally it will not be amiss to refer 

 in this place to the succession established by the Swiss geologists. 

 According to Miihlberg,^ the Glacial drifts of the Canton of Aargau 

 are as follows : 



Swiss Glacial Deposits. 

 1. Grundmorane or moraines \ Intense glacial conditions ; northern limits of the 



profondes / ice unknown 



1 See Geol. Mag. Vol. VIII., Dec. 1871, p. 545. 



"^ To avoid confusion I have in this table omitted the "high-level beaches," 

 which mark the pauses in the re-elevation of the land. They are referred to in my 

 second paper. I have of course left unmentioned the more recent raised beaches, 

 etc. It is with the Glacial beds proper that I am dealing. 



* Ueber die erratischen Bildungen im Aargau, etc. ; See Nature, vol. ii., p. 310. 

 Miihlberg's results agree with those obtained by M. Morlot, see Edinb. New Phil. 

 Journal, 1855, p. 14, and Antiquity of Man, p. 320. 



