306 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



schists occupied the centre ov crest of this structure. From 

 the centre of this fan, the pushing forces had exerted them- 

 selves in a north-westerly and south-easterly direction, and 

 the rocks had been plicated into deep isoclinal folds respec- 

 tively, pointing away from tlie central axis in these directions. 

 Many of these folds had been dragged forward or pushed over as 

 if by some differential movement, which had resulted in the 

 production of strain-slips running in a parallel direction to the 

 lines of thrust. As a rule they were developed to a greater 

 degree of perfection in the finer argillaceous beds than in the 

 more arenaceous rocks. In a phyllite, for example, they were 

 often to be seen to an extent of eight or more to the inch, cutting 

 thi'ough an earlier foliation and sending the mica flakes into a 

 series of sigmoidal curves. In cases where further stretching 

 had to take place, actual rupture seems to have been the result, 

 and the plates of mica have been rearranged along the lines of 

 strain. These strain-slips are developed to perfection in the Ben 

 Lawers schist ; and it was maintained that they are the principal 

 factors which have determined the present distribution of our 

 Alpine flora, as the plants have been enabled to retain a footing 

 on rocks of this type. 



29th August, 1905. 



Mr. P. Ewing, F.L.S., President, in the chair. 



A Report on an excursion from Aberdour to Burntisland, by 

 Mr. Goodchild, F.G.S., F.Z.S., was submitted by Mr. John 

 Renwick, who also read reports on excursions to Luss (p. 296), 

 and Blackhouse and St. Fillans (p. 299). 



The President reported on an excursion to Cruach Ardran, 

 and Mr. A. Patience on one to Millport and Little Cumbrae. 



Mr. P. J. Bell showed specimens of Agriotypus armatus 

 (Curtis), an Aquatic Ichneumon, parasitic on the larvae of 

 Trichoptera. This remarkable insect was discovered by Henry 

 Walker on the Clyde, near Lanark, and was described by Curtis 

 in 1832. It does not appear to have been observed in this 

 country since its discovery until April, 1905, when Mr. Bell 

 found it in a stream four miles west of Bearsden. Mr. Bell 

 described it as parasitic on the larvae of several species of 

 caddis-fly. The female goes under water and deposits her eggs 



