48 BATHYMETRICAL SURVEY OF 



Loch Lubnaig originally extended to a point below Coireachrombie, 

 about three-quarters of a mile below its present outlet. This point has 

 been silted up by the detritus laid down by the Stank and Anie burns. 

 The original southern termination of the lake touched the rocky barrier 

 formed by the Leny grit. It is worthy of note also, that the level of 

 Loch Lubnaig has been lowered about 20 feet by the denuding action of 

 the river Leny. 



Loch Katrine. For a distance of 4 miles, west from Brenachoil Lodge 

 to Stronachlachar about the half of the total length of the loch this 

 lake has a comparatively flat bottom, enclosed by the 400-feet contour- 

 line. The deepest sounding in Loch Katrine, 495 feet, is at the eastern 

 limit of this basin, nearly due south of Brenachoil. The chart shows 

 that the soundings throughout this basin gradually increase in depth 

 eastwards to Brenachoil Lodge. The position of the deepest sounding 

 is of interest, seeing that the strata which form the floor of the lake at 

 this point consist of schistose micaceous grits, to the north-west of the 

 epidotic grits (" Green Beds ") and the Ben Ledi grits, the two latter 

 groups having formed the great rocky barrier at and above the outlet of 

 the lake. 



Near the upper end of the loch a rocky barrier crosses the lake from 

 Portnellan by the Black island to Rudha Maoil Mhir an-t Salainn. The 

 deepest sounding along this barrier is 90 feet, and the shallowest is 48 

 feet. On its lower side the 100-feet contour-line well-nigh crosses the 

 lake. Above it there is another basin over half a mile in length, the 

 greatest depth of which is 128 feet, immediately in front of the rocky 

 ridge just referred to. Westwards the lake shallows, and at its head 

 it has been silted up for a distance of half a mile by the alluvium laid 

 down by the Gyle river. 



Below Brenachoil Lodge the soundings show an uneven floor, due 

 probably to ridges of rock rather than to morainic deposits, if we may 

 judge from the geological features on both sides of the lake. Ellen's 

 isle is composed of epidotic grits (" Green Beds "), and the promon- 

 tories of Am Priosan partly of ' ' Green Beds ' ' and partly of Ben Ledi 

 grits. The promontory between the pier and the sluice is formed of 

 Ben Ledi grits. 



During the geological survey of that region several small faults were 

 found to cross Loch Katrine, but these are of minor importance, and 

 have produced locally a slight brecciation of the strata. It is a typical 

 example of a rock basin. The deepest sounding occurs in the front of 

 the great rocky barrier in the lower part of the lake, in accordance with 

 what we might naturally expect on the theory of glacial erosion. 

 Though the soundings prove the deepest part of the lake to be 131 feet 

 below sea-level, yet this depth is in proportion to the vast thickness of 

 the ice during the successive glaciations of the basin. 



Loch Achray. This lake forms one basin, the deepest part being 



