THE FRESH- WATER LOCHS OF SCOTLAND. 259 



and Loch Linnhe these muscovite-biotite gneisses have been mapped by 

 the Geological Survey. These schists and gneisses, which are supposed 

 to represent altered sediments, are traversed by numerous veins of 

 pegmatite and dykes of diorite, dolerite, and basalt. 



On the watershed between Glen Hurich and Glen Scaddle, on the 

 crest of Sgor Dhomhail (2915 feet), there is a mass of foliated granite, 

 and, further to the south-west, the later igneous intrusions of the 

 Strontian district may enter the Loch Shiel catchment basin. 



NOTES ON THE BIOLOGY OF THE LOCHS IN THE SHIEL DISTRICT. 

 By JAMES MURRAY. 



Of the six lochs surveyed, tow-nettings were taken in four, and a 

 shore-netting in a fifth. The biology presented little of special interest. 

 Diaptomus laciniatus was found in two of the lochs (Shiel and Eilt) ; 

 these are the most southerly lochs in which this northern species was 

 observed by the Lake Survey, though it has been recorded by Dr. Scott 

 from one loch (Loch Doon) much farther south. 



Loch Shiel. Owing to the great abundance of Holopedium, which 

 choked up the nets, it was difficult to collect other animals in any 

 numbers. The most plentiful animals were : Diaptomus gracilis, 

 Diaptomus laciniatus, Cyclops strenuus , Bosmina obtusirostris, Bytho- 

 trephes, Polyphemus, six species of pelagic Rotifers (including Flos- 

 cularia pelagica), and Dinobryoii. The plants noted were : Xanthidium 

 antilopeum, Staurastrum gracile, and Staurastrum braziliense. Lobelia 

 and LittnreUa were in flower at the upper end of the loch. 



Loch Dilate. As compared with Loch Shiel, the most notable 

 features of this loch were : the greater abundance of life, the absence of 

 Holopedium and Diaptomtw Jaciniatus, and the presence of Diaphajio- 

 soma brachyurum in considerable numbers. Among the organisms 

 observed were: Diaptomus gracilis, Cyclops strenuus, Synchceta 

 pectinate, Plcesoma truncata, Dinobryon, Peridiniu?n, two species of 

 Ceratium (C . hirundinella and C . cornutum), Anabce.ua flos aqua with 

 its adherent Vorticellce. 



Loch Eilt. Life was abundant, the characteristic animals being 

 Holopedium, Diaptomus laciniatus, Cyclops strenuus, Anurcea cochlearis, 

 Notholca longispina, and Polyarthra. Leptodora and Bythotrephes were 

 scarce. Bosmina obtusirostris and a variety approaching B. longispina 

 were seen. The brilliant red and blue Rotifer, Notops pygmceus, was 

 plentiful. Some immature specimens of Diaptomus probably belonged 

 to D. gracilis. On the mud in the deepest part of the loch were numbers 

 of a pretty little green larva of an insect, enclosed in transparent flask- 

 shaped cases. 



