( 419 ) 



XX. — A Bathymetrical and Geological Study of the Lakes of Snowdonia and Eastern 

 Carnarvonshire. By T. J. Jehu, M.B., B.Sc. (Edin.), M.A. (Camb.), F.G.S., late 

 Heriot Fellow of the University of Edinburgh. Communicated by Professor 

 James Gejkie. (With Eight Plates.) 



(Read December 16, 1901. Issued separately June 16, 1902. 



CONTENTS. 



PAGE 



I. Introduction, ... . . 419 



II. Previous Work on British Lakes, . 420 



III. Orographical Features of the Dis- 



trict, 423 



IV. Methods, 424 



PAGE 



V. Description of the Individual Lakes 



and their Surroundings, . . . 426 

 VI. General Summary of the Characters 



of the Lakes, ..... 448 



VII. Origin of the Lakes, .... 455 



I. Introduction. 



The study of lakes has received more attention on the Continent than it has in our 

 own country. The inland waters of France and Switzerland have been most carefully 

 surveyed, and in America accurate soundings of many of the lakes have been made by 

 the Geological Surveys. But until recent years this work has been almost altogether 

 neglected in Britain; the Government had considered it to be outside the function of 

 the Ordnance Survey, and though of importance to geological research, it has not been 

 undertaken by the Geological Survey. The absence of adequate knowledge concerning 

 the forms of the basins occupied by the lakes has been a serious obstacle to the geological 

 inquiry as to the mode of origin of these basins. But recently, in the English Lake 

 District and in Scotland, this obstacle has been removed to a great extent through the 

 work of geographers, who have carried out a very complete bathymetrical survey of 

 many of the lakes of those regions ; and the importance of this work has been 

 recognised by geologists. But in North Wales not only had no attempt been made to 

 ascertain the configuration of the lake-beds, but in many cases even the depths of the 

 lakes remained unknown. 



Messrs J. E. Marr and K. H. Adie, in a paper on " The Lakes of Snowdon " (Geol. 

 Mag., 1898, p. 51), expressed a wish that "some one would do for the lakes of North 

 Wales what Dr Mill has so admirably performed in the case of those of English 

 Lake-land." The writer has made an effort to supply this want, and the results of his 

 work are given in this memoir. Though the survey may not be so complete as that 

 carried out by Dr Mill on the English Lakes, it is hoped that it will be sufficiently 

 accurate to throw light on the question of the mode of origin of these lakes. 



TRANS. ROY. SOC. EDIN., VOL. XL. PART II. (NO. 20). 3 s 



