544 Geological Society : — 



the rock lay very near to the surface ; here the highest part of the 

 boss was barely covered. The rock is hardly to be distinguished 

 from that of the Narborough pit. The enlargement of the pit 

 south of En derby has exposed fresh sections of the junction of the 

 slate and syenite, which has been now traced along the whole length 

 of the pit from north to south, and some particulars are added to 

 the former description. 



The enlargement of certain of the pits hasdisplayed some interesting 

 sections of Boulder Clay resting upon the crystalline rocks. The 

 latter are not appreciably ice- worn. The fragments in the Boulder 

 Clay, identified by the author, were from the Carboniferous, Trias, 

 Jurassic (especially Lias), and Upper Cretaceous formations. They 

 indicated, in the main, a drift from a more or less north-easterly 

 direction. 



2. ' The Tarns of Lakeland.' By J. E. Marr, Esq., M.A., F.K.S., 



Sec.G.S. 



The author has examined several tarns of the English Lake 

 District. In those cases where the stream issues from the tarn 

 over solid rock, he finds either (1) direct evidence that the tarn 

 results from the blocking up of part of a pre-existing valley by drift, 

 causing the deflexion of the water to a direction different from that 

 of the original stream in this locality ; or (2) evidence which is 

 perfectly consistent with such an explanation of the origin of the 

 tarn. 



Under the circumstances he would submit that tarns cannot be 

 assumed to lie in rock-basins simply because the issuing stream 

 flows over solid rock (and this assumption has been made), but that 

 those who maintain the existence of such rock basins must prove 

 the occurrence of solid rock entirely around the tarn. 



3. ' Description of a New Instrument for Surveying by the Aid 

 of Photography, with some Observations upon the Applicability of 

 the Instrument to Geological Purposes/ By J. Bridges Lee, Esq., 

 M.A., F.G.S. 



The instrument described in this paper consists essentially of a 

 photographic camera fitted inside with a magnetic needle, which 

 carries a vertical transparent scale divided and numbered to 360°, 

 and also with cross fibres which intersect at right angles. The 

 fittings and adjustments of the instrument are of such a character 

 that the camera can be accurately levelled and directed towards any 

 point in a horizontal direction, and when a photograph is taken in 

 an ordinary way the bearing of the median vertical plane which 

 bisects the instrument through the photographic lens will be recorded 

 automatically on the face of the photograph. 



The vertical fibre (and its image on the photograph) serves as an 

 index to read the bearing ; and the same fibre marks by its shadow 

 a line right across the photograph, which marks the median vertical 

 plane on the image. The horizontal fibre is adjusted to mark on 

 the image the horizontal plane which bisects the photographic lens. 



