Hardman — On Soundings takoi in Lough Gill, SUgo. 473 



LXIX. — PEELnrnsrAUT Eepokt oisr Soui^DriSrGS takejt US' Lough Gill, 

 Sligo. By Edwaud T. Hakdhau-, F. C. S., &c., H. M. Geological 

 Survey. 



[Eead, June 13, 18S1.] 



A GEANT of fifteen pounds having been voted by tbe Ptoyal Irish Aca- 

 demy towards carrying out the above object, the work was entered on 

 during a part of last year (1880). Owing to various circiimstances it 

 was not commenced until somewhat late in the season, but advantage 

 was taken of a continuance of favourable weather to obtain a great 

 many soundings. These have been as yet confined to lines of sections 

 along and across the lake, and in some of the principal bays and inlets 

 of it, as well as depths ascertained around some of the various islands. 



In this way a good deal of information has been obtained as to the 

 form of the lake-bottom, and many interesting facts noted, which, 

 when more fully followed up, will, it is expected, help considerably 

 to elucidate the physical history of the lake. 



It is proposed this year to continue these soundings, and to en- 

 deavour to obtain a series of depths along the shores at regular 

 intervals from it. 



The principal section runs right along the centre of the lake from 

 end to end, beginning at the entrance of the River Garavogue, passing 

 by Church Island, and continuing on to Shriif Bay. The depths 

 along this line are considerable in some places ; and one thing very 

 noticeable is a tendency to very sudden differences of level in short 

 distances. It is not uncommon to find within a distance of 400 feet a 

 difference of depth of 30 feet or more. 



The principal depths on this section are : — Between Cottage 

 Island and Church Island, 65 feet; one mile from the latter island, 

 96-38 feet; a little further on eastward, 97-6 and 99 feet; then 105 

 and 116 feet, the last being the greatest depth yet found in the lake. 

 This lies a little more than one mile from the east end of Church 

 Island, and one mile and three-quarters from the east end of the 

 lake. From this point to the end of the section at Shriff Bay the 

 lake shallows again. 



It should be noted that the depths given here are those actually 

 taken. But as the water was at the time exceptionally low, and at 

 least ten feet below its ordinary winter level, it would be necessary 

 to add five feet for the average depths of the lake. The greatest 

 depth would, therefore, be about 121 feet. 



Another section was taken parallel to the last, and south of it, 

 along the shore, from Aghamore Bay, through Goat Island, to Slish 

 "Wood. The depths along this line are moderate as far as Goat 

 Island, where they suddenly increase. The northern shore of this 

 island shelves down very rapidly, forming a deep cliff, which, at 

 thirty yards from the shore, is 63 feet in depth. Further on the 



