1818.] Royal Society of Edinburgh. 145 



metal converted into a muriate, whilst a portion of water, nearly 

 equal to one-sixth the weight of the dry sal-ammoniac, made its 

 appearance. To this part of the paper is subjoined the descrip- 

 tion and drawing of a new, simple, and accurate exploding eudio- 

 meter, which the Doctor employed for analyzing the gaseous 

 products of the above experiments. 



At the same meeting, a paper by Dr. Fergusson, inspector of 

 hospitals, was read on the Mud Volcanoes of the Island of Tri- 

 nidad. 



In the beginning of the year 1816, this gentleman was em- 

 ployed, along with the deputy quarter-master general of the 

 colonies, and an officer of rank in the engineer department, to 

 make a survey of the military stations in the West Indies, during 

 which their attention was attracted to this extraordinary pheno- 

 menon in a district of country that had always been considered, 

 according to their information, as strictly alluvial. It appeared 

 to them to be so highly illustrative of the minor incipient degrees 

 of volcanic agency in the formation of argillaceous hills, that they 

 thought it would be right to mention it in their report, and Dr. 

 Fergusson was deputed to draw up the statement. 



This gentleman found that the eruptions of these semi-volca- 

 noes, two in number, which are situated on a narrow tongue 

 of land which points directly into one of the mouths of the 

 Oronoko on the Main, about 12 or 15 miles off, at the southern 

 extremity of Trinidad, and not far from the celebrated Pitch 

 Lake, are at all times quite cold. That the matter ordinarily 

 thrown out consisted of argillaceous earth mixed with saltwater, 

 about as salt as the water in the neighbouring Gulph of Paria ; 

 but though cold at all times, that pyritic fragments were occa- 

 sionally ejected along with the argillaceous earth. They also 

 observed, that several mounts in the vicinity possessed the same 

 character in all respects as the semi-volcanoes then in activity, 

 having all the marks, except the actual eruption, of having been 

 raised through a similar process to their existing altitude, of 

 about a hundred feet; and that the trees around them were of the 

 kind that are usually found near lagoons and salt marshes. The 

 nature of the duties on which they were employed did not permit 

 their attempting any analysis of the air, water, or earths, 

 furnished by the eruptions. 



Nov. 24. — A general meeting of the Society having been held 

 for the election of office-bearers, the following gentlemen were 

 chosen : 



President. — Sir James Hall, Bart. 



Vice-Presidents. — Right Hon. Lord Gray and Lord Glenlee. 



Secretary. — Professor Play fair. 



Treasurer. — Mr. Bonar. 



Keeper of the Museum. — Thomas Allan, Esq. 



President of the Physical Class. — Sir George Mackenzie, 

 Bart. 



Vol. XI. N° II. K 



