Different kinds of Coal for the purpose of Illumination. 49 



The following are the results with different kinds of bur- 

 ners, the trials having been conducted with the view of ascer- 

 taining the illuminating power by these burners : — 



From the above it will be seen that the escapes ai'e very 

 nearly as the roots of the pressures. 



(To he concluded in our next Number.) 



On the Parallel Boadsof Lochaber. By JAMES THOMSON, Jun., 

 M.A., Glasgow College. Communicated by the Author.* 



The Parallel Roads, Shelves, or Terraces, of Lochaber, 

 constitute a wonderful inscription, traced by the hand of 

 Nature, over the surface of a wide range of mountains and 

 glens. To interpret this writing, and to disclose the story 

 which these mysterious but clearly-marked chai'acters trans- 

 mit, has long been an object of much interest, as well as of 

 great perplexity, to geologists. As yet, however, no one has 

 succeeded in arriving at an explanation of the subject, which, 

 after having undergone the scrutiny of others, has given 

 general satisfaction ; and scientific men are still, perhaps, as 

 much divided in opinion as ever in regard to the nature of 

 the operations by which they suppose these terraces to have 

 been produced. Two papers, taking different sides on this 

 question, have appeared in the last two numbers of Jame- 

 son's Philosophical Journal, — the first by Mr David Milne, 



■* Read before the Ifoyal Society of Edinburgh, 6th March 1848. 

 On reading this pajjer, consult the Map of the Shelves or Parallel Itoads 

 of Lochaber, in vol. xliv. of this Journal. 



VOL. XLV. NO. LXXXIX. — JULY 1848. D 



