ARCTIC PLANTS IN OLD LAKE DEPOSITS OF SCOTLAND 51 



The course of deposits in Corstorphine Lake from first 

 to last would be : 



1. Boulder clay of unknown thickness, but irregular ; as 

 it sometimes comes to the surface, and at other times sinks 

 out of reach of the sewer cutting. 



2. A coarse gray sand, with occasional stones, evidently 

 the residue of the boulder clay, from which the finer silt had 

 been washed away. It was always wet, and doubtless acted 

 as an underground drain to carry off the surplus rain-water, 

 which sank down through the upper lake marl, etc., but 

 could not go through the impervious boulder clay, and 

 flowed along the top of it to lower levels. 



3. Fine laminated clay, red like tile or brick clay. 

 This is evidently the finer silt washed out from the boulder 

 clay of the grounds surrounding the hollow in which the 

 lake lay. It was free from peat and marl, and had nothing 

 organic in it except shreds of vegetable tissue, the remains 

 of rootlets of water-plants. 



4. The Arctic Plant Drift-beds. Sometimes of pure drift, 

 with no clay or mud, but oftenest as layers of fine clay, mud, 

 or silt, with the leaves in thin layers ; at other times with 

 the leaves scattered singly through the deposits, sometimes 

 with much debris, consisting of vegetable fibres, dried root- 

 lets, or epidermis of water-plants of which the soft tissue had 

 decayed and only the coriaceous rind had been left, some- 

 times with quantities of twigs an inch or so in length, 

 stripped of bark, rounded at the ends, and water-worn, 

 evidently the shore wrack of the lake. Fruits of the Arctic 

 Willows are frequent, sometimes with the cottony wool still 

 inside them, and sometimes with the stigmas projecting. 

 As Arctic Willows are land-plants, these must have grown 

 on the slopes of Corstorphine Hill, or on the knowes on the 

 south side of the lake ; and been wafted by the wind, or 

 drifted by water, into the middle of the lake, and finally 

 have sunk in its waters. 



5. These Arctic plants are regarded as a proof of the 

 climate of Corstorphine having been 20 Fahr. colder than 

 at present, and that the glacial period was still in session in 

 this latitude. But the best things got in these Arctic plant- 

 beds were the remains of Apus glacialis, the crustacean 



