TRANSACTIONS OF SECTION E. 619 



feJcperimeuts undertaken by it, and of the aid supplied to inexperienced settlers. 

 The subject of plant immigration and plant breeding was touched upon, and 

 a summary given of the changes in life forms that have taken place during the last 

 thirty j'ears in the western half of the United States. 



o 



2. The Survey of the Scottislb Lochs : Suinmary of Work, 1902-1906. 



By James Murray. 



Since its institution by Sir John Murray and Mr. Laurence Pullar in 1002, 

 the bathymetrical survey of more than five hundred of the Scottish lochs has been 

 completed. Among these are all the great lakes of the country, and there remain 

 to be sounded only about a hundred lochs, of secondary importance. 



Geographical liesidts.— The Scotch lakes, with very few exceptions, are of 

 elongate narrow form, and none are really great lakes, the largest approaching 

 24 miles in length. Yet many of the larger lochs exceed 500 feet in depth, 

 and Loch Morar exceeds 1,000 feet. Such depths are comparable with those of 

 the deepest lakes of Europe, and as these are for the most part of much greater 

 breadth and superficial area, the Scotch lakes are relatively very deep. The 

 soundings iu general confirm the conclusions previously reached by the Scotch 

 geologists as to the origin of the lakes. Most of the great ones and a large 

 number of smaller ones have the U-shaped section which characterises lakes 

 hollowed out by glaciers. The usual deposit in all the lakes, great and small, is 

 a black peaty mud, the abundant organic matter partly originating in the lakes 

 and partly .entering the lakes from the peat bogs, from which much of the 

 water comes. The mineral constituents vary with the locality, and micaceous and 

 quartz sands take the place of the black mud iu places. There are also yellow, 

 grey, and red clays, the origin of which has not been studied. It is not known 

 whether these are old strata exposed in the beds of the lakes, or modern deposits 

 at present being formed. The water of most of the lakes is brown and peaty. 



Biology. — The outstanding facts which have so far appeared are: (1) The 

 great prominence in the lakes in summer of conspicuous species of Crustacea 

 belonging to the Arctic association of plankton species ; (2) The exceeding 

 richness of the phytoplankton, especially in desmids, a fact first brought clearly 

 out by Messrs. W. and G. S.' West ; (3) The abundance of certain orders of 

 microscopic animals (Rotifera and Tardigrada) at the lake margins. The third 

 fact probably indicates merely the habitual neglect of those orders in lake studies. 



Fhysics. — The physical observations dealt mainly with temperatures and 

 Seiches. Serial temperatures at all depths were taken in all the lochs surveyed, 

 and in Loch Ness an extensive series of simultaneous observations at different 

 parts of the lake was made. The chief outcome of these was the detection of a 

 remarkable seiche (the Internal Seiche). 



Seiches. — Observations of seiches were made in many lakes by various members 

 of the staff. The first seiche was noticed iu Loch Treig, by Dr. Johnston and 

 Mr. Parsons, in 1902. The detailed study of a few lakes has been undertaken by 

 Professor Ghrystal, assisted by Mr. Wedderburn and others. Professor Ghrystal 

 has made important contributions to the mathematical theory of seiches, and has 

 besides eflected great improvements in the apparatus for observing seiches. The 

 most important of these is the applying of the statoscope to the recording of seiches, 

 by which an exceedingly delicate tracing is obtained. 



The Internal Seiche. — Stripped of complexities, the internal seiche may be 

 explained as arising thus : In autumn, when the lake has begun to cool, there is a 

 .sharp demarcation between an upper, warmer layer of water, and the deeper, colder 

 layer, which only experiences secular changes of temperature. At this limit, 

 which the Germans call the Sprungschicht, a change of sevei-al degrees may occur 

 within a few feet. The efiect of a long-continued gale, as shown by Sir John 

 Murray, is to cause an inclination of the upper isotherms of the loch, the depth 

 to which they are affected being regulated by the strength and duration of the 

 wind. At the termination of a gale which has sufficed to cause au inclination 



