GEOLOGY. 241 



drift." This structure- may frequently be seen in polished sections of 

 clay-slates, and also, in a form modified through metamorphism, in 

 many mica-schists. From a consideration of the facts revealed by an 

 examination of those rocks, the author concluded that mica-schist is of 

 sedimentary origin, metamorphosed after deposition, and sometimes 

 after the production of cleavage and other physical changes, and that 

 the bands of different minerals represent the planes of original depo- 

 sition. 



Origin of Flint Nodules in Clialk. In a recent discussion on this 

 subject in the London Chemical Society, Dr. Church claimed that the 

 flints in chalk could be traced to water holding silica in solution. Dur- 

 ing the percolation of such water through beds of chalk, the silica be- 

 came separated, and the carbonate of lime took its place in the water 

 thus deprived of its silica. An interesting example of the deposition 

 of silica in the form of chalcedony took place within a comparatively 

 recent date, geologically speaking. About the year 1400, a basket of 

 hen's eggs had been left in a chalk pit at Winchester, England, and 

 this basket was lately found covered up with broken chalk. The or- 

 ganic matter and the shell of the eggs had entirely disappeared and 

 their places were occupied with the semi-transparent variety of silica, 

 chalcedony. Silica was also deposited upon the willow twigs compos- 

 ing the basket, forming a crust of silica. 



The Progressive Development of Organic Life. At a meeting of 

 the British Association, 1863, Professor Harkness stated, that the re- 

 mains of reptiles, and the impressions of feet discovered within the last 

 few years in the sandstones of the northeast of Scotland, afforded evi- 

 dence of forms belonging to a period far more remote than any of 

 which palaeontology had as yet taken cognizance ; upon this, Sir C. 

 Lyell remarked, that if the facts put forward were true, one of the 

 greatest blows had been struck at the theory of development, as gener- 

 ally understood, that could possibly have been dealt. There had been 

 too great an inclination on the part of geological discoverers to assume 

 that any given form of animal entered into this planet at the period of 

 the rock in which it happened to be found ; and the warning he had 

 constantly given against this tendency had been interpreted as a much 

 stronger protest against the doctrine of progression than it ought to 

 have been. When the first of these telerpetons, being a new form, was 

 announced to be found in a rock, reported on good authority to be 

 Devonian, or, at any rate, palaeozoic, he did feel a pleasure in the re- 

 buke such a fact gave to the doctrine that no reptiles existed at that 

 period. It always appeared to him unphilosophical, merely because 

 we knew nothing of the vertebrate life of that period, to assume, there- 

 fore, that no reptiles existed older than the trias. But afterwards, 

 when it was discovered that the Stagonolepis, a supposed fish, was a 

 crocodilian reptile, and that some of the other forms were the same as 

 those of the crocodiles now living in the Ganges, he began seriously 

 to doubt whether his friends had assigned a true position in the geolo- 

 gical series to these beds. Now, he saw clearly from the investigations 

 that these must be admitted to be a consecutive regular series from un- 

 questionably Lower Red beds containing the well-known fishes of the 

 Old Red forms that were known to be carboniferous up to the beds 

 containing those reptiles. 



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