James Geikie — On Changes of Climate. 65 



the drifts in the neighbourhood of Glasgow. Mr. J. Bennie gives,' 

 amongst a number of others, a section of the " surface " at Blairdardie, 

 which is as follows : — 



1. Surface soil 4^ feet. 



2. Blue clay 9 



3. Hard stony clay (Till) 69 



4. Sand with a few shells 3 



5. Stony clay and boulders (Till) 46| 



6. Mud and running sand (quicksand) 11 



7. Hard clay, boulders, and broken rock (Till) 27 



170 „ 

 Mr. Whittlesey figures a section taken quite close to Lake Michigan, 

 which shows the following succession. (The thicknesses are not 

 given.) 



Eed clay and red hardpan. 



Yellow sandy clay. 



White and purple clay, mixed colours in part. 



Gravel. 



Elue laminated clay passing down into purple hardpan [apparently very thick]. 



The State geologists of Illinois ^ give the following section of the 

 drift afforded by a shaft sunk in the city of Bloomington : 



1. Surface soil and brown clay 10 feet. 



2. Blue clay 40 „ 



3. Gravelly hardpan 60 „ 



4. Black mould, with pieces of wood, etc 13 „ 



5. Hardpan and clay 89 ,, 



6. Black mould, etc 6 „ 



7. Blue clay 34 „ 



8. Quicksand, bulf and drab in colour, and containing fossil shells 2 „ 



9. Clay shale (Coal-measures) 



254 „ 



I have referred to these American sections because, as it seems to 

 me, they are in all probability the equivalents of the inter-Glacial 

 deposits of the Scottish Till. It is quite clear from Mr. Whittlesey's 

 paper that the freshwater beds with organic remains are of older 

 date than the mounds of sand and gravel and erratic blocks which 

 overlie the unmodified drift; and Mr. Whittlesey himself believes 

 the plants to represent the flora that characterized North America 

 during or previous to the Glacial epoch. Dr. J. S. Newberry, refer- 

 ring to these and similar phenomena, says, "It has long been known 

 that, in many parts of the valley of the Mississippi, wells penetrat- 

 ing twenty, thirty, or more feet, the superficial formations of drifted 

 materials, clays and sands, with gravels and boulders brought from 

 the far north, encounter sticks, logs, stumps, and sometimes a distinct 

 carbonaceous soil." These vegetable remains, he continues, " form 

 a distinct line of demarcation between the older and newer drift 

 deposits. In or above the horizon of this ancient soil have been 

 found numerous animal remains, ElejjJias, Mastodon, Castoroicles (the 

 great extinct beaver), and some others."^ 



1 On the Surface Geology of the District round Glasgow, etc. Glasgow Geol. 

 Trans, vol. iii., part i. 



2 See Geology of Illinois, vol. iv., p. 179. The "shells" are of fresh-water species. 



3 See Nature, June 22, 1871, p. 155. 



VOL. IX. — NO. XCII. 6 



