PKOCEEDINQS OF GEOLOGICAL SOCIETIES. 



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minerals. Near Loch Tlioru the rocks become compact greenstone, and 

 dark-coloured porphyry. When the excursionists arrived at the eastern 

 extremity of the Loch, they came suddenly upon a fine section of the 

 "Ballagan limestones," tilted up nearly vertical, with regular divisions 

 of shales, which have lost much of their schistose character, and are regu- 

 larly traversed by thin veins of calcareous spar — apparently a variety of 

 satin spar. The remarkable uplifting of these strata is the effect of a trap 

 dyke, visible close beside them, also a portion of an overlying sandstone 

 converted into "kingie " (a mining term for indurated sandstone) by igneous 

 action. At the opposite extremity another trap dyke appears, which ap- 

 parently has effected this change in the sandstone. These sandstone 

 beds are at the same angle as the other strata. The burn below exhibits 

 the Old Red Sandstone in situ, and Eed Marl clays also much altered by 

 igneous action, with a number of fine specimens of lied Sandstone con- 

 glomerates. In going up tlie burn the route is over a bed of similar lime- 

 stone, and the district is well worthy of future detailed examination. One 

 remarkable feature of these Ballagan beds was the rounding of the vertical 

 limestones, being of a flattened spherical shape, evidently the result of 

 weathering and scaling off at the exposed surfaces. These Ballagan beds 

 occur some miles distant at Ballagan, Campsie Hills, and a range of fine 

 sections occurs at Auchenreoch Glen, Dumbarton; with this difference, 

 at Loch Thorn the crystallized veins of calcareous spar are carbonate of 

 lime, while at Auchenreoch and "Ballagan" they are sulphate of lime 

 (gypsum). Loch Thorn is a fine sheet of water, partly artificial and partly 

 natural. It supplies Greenock and its works with water. 



Since the discovery of the Ballagan beds at Loch Thorn, at the time 

 of the excursion, one of the members has visited the district, and having 

 gone a considerable distance up the burn, reports that other important ap- 

 pearances of the Ballagan strata present themselves in very fine sections, 

 and that the igneous cause of their upheaval and vertical position is exhi- 

 bited lower down the burn than was suspected during the first rapid view 

 taken of the strata. No doubt a more searching investigation will take 

 place during the summer, and should any imjjortant facts present them- 

 selves in relation to the relative positioii, etc., of the Ballagan beds with 

 the Old Hed Sandstone and coal-measures, the information will be for- 

 warded to the ' Geologist.' 



EoYAL Society. — IQth June. — " On the Loess of the Valleys of N. of 

 France and S. of England." By J. Prestwich, Esq., F.E.S. During a re- 

 cent visit to Erance the author made observations which have enabled him 

 to draw conclusions as to the formation of the Loess. In this communi- 

 cation the author first refers to the Loess of the Hhiue, concurring with 

 Sir Charles Lyell in attributing its origin to river inundations, but draws 

 different conclusions as to the mode and circumstances of its deposit. 



The greatest difficulty that has been felt in attempting to understand 

 the spread of the Loess in England and France has been the great differ- 

 ence of the levels at which they are found, these often being from 100 to 

 300 feet above the present river-courses — heights to which no river-inun- 

 dations could attain in the present valleys. But of the former existence 

 of less deeply-excavated valleys in the present valley-sites, the covering of 

 Loess might lead to the inference ; and notwithstanding the extension of 

 the Loess over the loftier ground flanking the valleys, such areas appear 

 to be always bounded by higher hills, forming a barrier restricting the limits 

 of the floods. The author's opinion is that the Loess is, like the high- and 

 low-level gravels, always connected with river-valleys ; and if, instead of 

 starting at the present low-levels, the ancient valleys be taken at the level 



^OL. Y. 2 M 



