116 /. B. Dakyns—Note on the Green and Shiddaw Slates. not. Where several cracks existed, the green bands soon united, and the entire crystal was changed. In another instance the change commenced at the surface and extended inwards, till only the central portion was left unaltered; or again, the change proceeded in both ways simultaneously. The evidence afforded by the study of these sections is so com- plete, that there cannot, I think, be a doubt as to the conclusion to be drawn. The rock-specimen is from Hailstone Hill, and is a well-crystallized, nearly black, basalt, of rather coarser grain than the mass of the rock, and a "power" of one inch is sufficient for its examination when cut into a thin section. One point which deserves more attention than it has hitherto received, is the alteration which rocks have undergone subsequently to their consolidation, it is one of the great difficulties the petrolo- gist has to contend with, but it is not insuperable. The polariscope will generally indicate the occurrence of metamorphism, and a careful search for the least altered portions of a rock may enable the enquirer to learn the history of the change, and thus gain a more correct knowledge of the original rock. It is clear, for example, that Olivine was one of the original constituents of the basalt above described, for its pseudomorphs occur in every part of the district in which the rock is found. I venture to hope that the insertion of these observations in your valuable Journal may contribute in some slight degree to show that a microscopical analysis may be advantageously employed when a chemical analysis is impossible, and that the origin and structure of many rocks and minerals will not be accurately known till the microscope is far more extensively used than it hitherto has been by Geologists and Mineralogists. VI.—ADDITIONAL NOTE ON THE UNCONFOKMITY BETWEEN THE GREEN AND SKIDDAW SLATES. By J. K. DAKYNS, M.A., of the Geological Survey of England and "Wales. fPHE Unconformity between the Green and Skiddaw Slates, which _|_ I pointed out in the last number of the GEOLOGICAL MAGA- ZINE, (see p. 56) as exhibited between Grange in Borrowdale and Dale Head will, I think, explain satisfactorily the Geology of Der- wentwater. If anyone refers to Euthven's map of the Lake Country, (edition of 1855,) he will see the division between the two sets of beds drawn between Castlehead and Castlerigg, and thence in a south-west direction on the north side of Eobinson. This is incorrect. Eobin- Bon and Hindscarth are both composed of Skiddaw Slates, and Castlehead, to the best of my belief, of Greenstone. The line I drew runs from Lowdore by the bridge at Grange to Dale Head, which is roughly parallel to Euthven's line, but nearly a mile and a half distant from it to the south-east. v Thus it will be seen that while the western side of Derwentwater /. R. Dakyns—Note on the Green and Skiddaw Slates. 117 consists of hills of Skiddaw Slates, the eastern side, with the exception of a narrow strip near the water about Lowdore, is com- posed of hills of the volcanic series. Now were the two sets of beds conformable, as they have hitherto been generally considered to be, and as they have always been mapped, this would require a fault along the lake with an enormous throw, which would, doubt- less, highly delight those persons who, having surveyed but little, fancy there are always faults along valleys, especially if the valleys are occupied by lakes. If, however, the two sets of beds are un- conformable, of which I have very little doubt, then the structure of the country is perfectly intelligible, without calling in the aid of a fault, which, however, may exist for aught I know. As I have alluded to those theorists who used to explain lakes as lying in open fissures caused by faults, of the existence of which fissures there is not a particle of positive evidence—a race of Geo- logists, which I fear is not yet extinct, though they doubtless received their death-blow in the excellent paper by Professor Ramsay on the origin of lakes—I may as well say that I saw several instances in the Lake Country of lakes lying in true rock basins; for instance, Thirlmere lies in a rock basin. Again, there can be no doubt, from the great spread of alluvium, that part of Borrowdale above the Bowder Stone was once occupied by a lake as far as Seatoller certainly, which lake probably split into two arms running some way up the two valleys of Stonethwaite and Sea- thwaite. Now this old lake was enclosed in a rock basin, the well glaciated barrier of which crosses the valley a little south of the Bowder Stone and blocks it up, save where the stream has cut a narrow channel for itself. The gradual silting up of the lakes is also well exhibited in many of the still existing lakes. Derwentwater and Bassenthwaite are separated by a wide, low alluvial flat, but little higher than the levels of the lakes, which doubtless once formed one great lake reaching as far as Grange. Similarly, Buttermere and Crummock once formed one lake, which reached more than half a mile higher up the valley. urornxcjss O:F MEMOIBS. TBANSACTIONS OF THE MANCHESTER GEOLOGICAL SOCIETY. Vol. vii., Part 9, and Vol. viii., Part 1. 1868. LET ix. contains a paper by Mr. P. S. Eeid, on some copper, iron, and other mineral deposits of the Maritime Alps, in the districts Fof St. Sauveur, Valdeblore, and St. Martin de Lantosque. The mines of St. Sauveur and Valdeblore are situated on the French and Italian frontier, about 35 miles from the town of Nice. The predominant formation is Jurassic Limestone, under which and reposing on Mica Schists are metamorphic rocks, answering in a great measure to our New Eed Sandstone formation, and in these the principal deposits of copper, now described, are found..