PEOCEEDINQS OF GEOLOGICAL SOCIETIES. 
265 
minerals. jN"ear Loch Thorn 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 ''kingle " (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 sandstoae. These sandstone 
beds are at the same angle as the other strata. The burn below exhibits 
the Old Eed Sandstone in situ, and Eed Marl clays also much altered by 
igneous action, with a number of fine specimens of Red Sandstone con-, 
glomerates. In going up the 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 ofi" 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 wiU take 
place during the summer, and should any important facts present them- 
selves in relation to the relative position, etc., of the Ballagan beds with 
the Old Red Sandstone and coal-measures, the information will be for- 
warded to the ' Geologist.' 
RoTAL Society. — V^th June. — " On the Loess of the Valleys of N. of 
France and S. of England." By J. Prestwich, Esq., F.R.S. During a re- 
cent visit to France 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 Rhine, 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 valle3'S, 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-vaUeys ; and if, instead of 
starting at the present low-levels, the ancient valleys be taken at the level 
VOL. Y. 2 M 
