Yol. 62.] TAKNS OF THE CANTON TICINO. 167 



all events, he ' saw difficulties.' A glance at the geological map of 

 Switzerland shows that these lakes lie along the outcrop of certain 

 Utlesozoic limestones. It is also noticeable that, if traced westwards 

 from the Airolo district, other lakes, such as the Engstlensee and 

 the Trubsee, are found to be situated on the outcrop of the same 

 rocks. Furthermore, it is obvious that many of the chief valleys and 

 passes, such as the Yal Bedretto and the jSTufenen Pass, or again 

 the Urserenthal and the Eurka Pass, have been excavated along the 

 strike of these calcareous rocks. 



In noting these facts, I felt convinced that the occurrence of so 

 many tarns along the outcrop of the same beds as those in which 

 the valleys and passes had been excavated, must point to something 

 more than mere chance coincidence. An especial interest attaches 

 to these lakes, inasmuch as they include the group the origin of 

 which Prof. Bonney has hesitatingly conceded to ice-erosion. I 

 have, therefore, devoted portions of my summer-holidays during 

 the past few years to their investigation. 



I began work on the western group of lakes, which lie to the 

 west and north of the Titlis. A preliminary survey showed that 

 no definite conclusions could be reached, without some knowledge 

 of the depth and general form of the lakes ; none of these lakes, 

 however, had been sounded, and this work yet remained to be 

 done. One great obstacle presented itself to the immediate accom- 

 plishment of this preliminary step, in the fact that the majority of 

 the tarns are destitute of boats. After consideration, I abandoned 

 the idea of a portable boat, as the lakes are seldom free from wind 

 after sunrise, and the accuracy of the soundings obtained from a 

 drifting coracle seemed to me to leave a good deal to be desired. 



Eventually, with the assistance of a grant from the Government- 

 Grant Committee of the Royal Society, I succeeded in constructing 

 a sounding-machine which could be used from the banks without a 

 boat, capable of yielding very accurate results, being self-registering 

 both as to the depth and the positions of the soundings. With this 

 instrument I made a detailed survey of the group of lakes of 

 the Yal-Piora district, and later included other important tarns 

 of the Canton Ticino. In the work of soundiug these tarns 

 I received great assistance from my friends, Miss Violet Waine- 

 wright, Mr. Haworth Moberly, and Dr. Ernest Kingscote, to each 

 and all of whom I tender my sincere thanks, not only for the 

 results that they accomplished, but for the way in which, by their 

 ever-ready help and interest, they converted a somewhat tedious 

 piece of work into a summer-recreation. 



In the following pages I have endeavoured to bring together such 

 facts as seem to bear on the origin of these lakes ; but^I have not 

 yet had the opportunity of visiting all the tarns in the Canton 

 Ticino, and my remarks must therefore be taken to apply only 

 to those lakes which are actually described. 



