EXCURSION XVI. 



have been made by Mr. Magnus M. Tait, F.C.S., formerly 

 assistant to Dr. Anderson, Professor of Chemistry, Glasgow 

 University, now of Messrs. Vivian's Works, Swansea : 



Claystone. 



Silica, 

 Alumina, . 

 Potash, . 

 Soda, 

 Magnesia, 

 Oxide of iron, 

 Lime, 

 Water, . 

 Loss, 



Pitchstone. 



Silica, 



Alumina, 



Soda, 



Potash, . . . 

 Water and organic matter, 

 Magnesia, .... 

 Lime, ..... 

 Oxide of iron, .... 

 Loss, ..... 



72-50 

 11-53 

 5-24 

 3-37 

 2-72 

 2-06 

 1-79 

 0-70 

 0-09 



100-00 



66-03 

 12-55 

 5-02 

 4-13 

 4-20 

 2-33 

 2-80 

 2-75 

 0-19 



100-00 



96. A walk in the late afternoon from Black water-foot to 

 Lag, across Leac-a-Bhreac, forms a pleasant close to the day's 

 excursion to King's Cove. Leac-a-Bhreac, or the Brown 

 Hill, is a high, round ridge, with steep seaward front, and 

 long inland extension, lying between Kilpatrick, near Black 

 water-foot, and the mouth of Slaodridh Water. It is com- 

 posed of felspar porphyry, being the largest mass of this rock 

 in the island. The base is a gray, or bluish gray, compact 

 felspar, sometimes passing into a jaspideous hornstone, often 

 iron-shot, and the imbedded crystals, glassy felspar; smoky 

 quartz also occurs in round bits, like worn crystals, and the 

 rock affects the columnar form, the columns having flat 



