July 13, 1888.] 



SCIENTIFIC NEWS. 



41 



cooled magma of the volcano. Moreover, such rocks 

 come from depths where they have not been affected by 

 alterations of a secondary nature. 



He then gave a classification of the varieties of ejected 

 blocks. The tertiary rocks are but slightly metamor- 

 phosed, whilst the limestones of cretaceous or earlier 

 age afford an almost unlimited series of mineral aggre- 

 gates. Physical changes have converted them into car- 

 bonaceous and saccharoidal marbles ; next oxides and 

 aluminates have separated, and silicates have been intro- 

 duced. Such rocks come under the definition of acci- 

 dental ejectamenta. They are only ejected when the 

 apex of the crater-cavity, formed by an explosive erup- 

 tion, extends below the platform of the volcano into the 

 underlying rocks. He then traced the history of the 

 eruptions of Somma-Vesuvius through divers phases, 

 showing that it was only at a comparatively late period 

 that limestone fragments were blown out, though this 

 had taken place long before the Plinian eruption. The 

 stratified limestones have been chosen for the first part 

 of this paper, because their original lithological structure 

 acts as a guide as we proceed from a normal limestone to 

 its extreme modifications. 



Part I. — The character of the limestones which under- 

 lie the platform of Vesuvius may be studied in the 

 peninsula of Sorrento, where the mass attains a thick- 

 ness of 4,700 feet. They are magnesian in varying pro- 

 portions. A table was given showing twenty-seven 

 analyses, made principally by Ricciardi, the amount of 

 MgO ranging from 1 to 22 per cent. Silica rarely 

 exceeds 2 or 3 per cent., whereas in the greater number 

 of limestones it is absent. The bituminous matter, 

 though a povveiful colouring agent, usually exists in 

 quantities too small for estimation, but sometimes reaches 

 3 per cent. Such are the materials out of which the 

 extraordinary series of silicate-compounds have been 

 developed, and as these materials of themselves could 

 not form peridotes, micas, pyroxenes, etc., it is clear that 

 the silica, alumina, iron, fluorine, etc., must have been 

 introduced from without, viz., from the neighbouring 

 igneous magma. The author then discussed the question 

 of the probable methods, being inclined to favour the 

 notion of vapour in combination with acid gases. 



The bulk of the paper was occupied with a detailed 

 description of the microscopic structure of these stratified 

 limestones and their derivatives. The author remarked 

 that the same metamorphic changes may be traced on a 

 much grander scale amongst the ejected blocks, and 

 hinted at the similarity of these changes to those of 

 contact-phenomena as seen elsewhere, and even of 

 regional metamorphism, the two main factors to be con- 

 sidered being the composition of the rock to be acted 

 upon and that of the magma acting. 



The changes which ensue in an impure limestone are, 

 in the first place, the carbonisation of the bituminous 

 contents, which are converted into graphite ; and a kind 

 of recrystallisation, approaching the saccharoidal struc- 

 ture, seems to have taken place, although the stratifica- 

 tion, etc., is preserved. A few grains of peridote now 

 begin to make their appearance, chiefly as inclusions 

 within the calcite crystals, and thus by degrees the 

 results already recorded are effected. In the early 

 stages only is the metamorphism selective. The order 

 in which the new minerals seem to develop is the fol- 

 lowing : — 



(1) Peridote, Periclase, Humite. 



(2) Spinel, Mica, Fluorite, Galena, Pyrites, Wollas- 



tonite. 



(3) Garnet, Idocrase, Nepheline, Sodalite, Felspar. 

 Many of these minerals are crowded with microliths, 



which there is reason to believe consist of pyroxene. 



MANCHESTER CRYPTOGAMIC SOCIETY. 

 At the meeting held on the 18th June, Dr. B. Carring- 

 ton, F.R.S.E., in the chair, Mr. W. H. Pearson exhibited 

 a collection of mosses and lichens from Jamaica, which 

 had been fowarded by Mr. Cockshot for the Society's in- 

 spection. Amongst the lichens Mr. Bowers pointed out 

 specimens of Parmelia pcrlata in fruit. This is a British 

 species, but is always found barren in this country. The 

 collection had been made by Miss Eglinton in the neigh- 

 bourhood of Kingston, Jamaica. Mr. Pearson also ex- 

 hibited a collection of Hepaticae from New South Wales, 

 collected by Mr. Thomas Whitelegge, of the Australian 

 Museum. These had been described, and drawings made 

 by Dr. Carrington and himself, and published by the Lin- 

 naean Society of New South Wales. The authors pre- 

 sented a copy to the Cryptogamic 'Society. Another 

 interesting collection shown by Mr. Pearson was a series 

 of specimens of the Hepaticae of Queensland, sent by Mr. 

 C. Wild, a former member of the Society. They had 

 been identified for the most part by Herr Stephani, and 

 two had been named by him in honour of the discoverer, 

 Mr. C. Wild, now resident in Queensland. 



Mr. F. Bowers exhibited specimens of the Hepaticae 

 collected by himself during the excursion of the Yorkshire 

 naturalists in the Saddleworth district on Saturday last ; 

 and Mr. Pearson exhibited specimens of Marsupclla 

 stablcii which he had found during Whitsun week near 

 Cwm Idwal, North Wales, this being a new station for 

 this rare hepatic. 



Mr. William Forster showed a pan of young ferns 

 from his fernery, which was most interesting, showing 

 as it did the reproduction of ferns without the inter- 

 vention of the developed spore (Apospory). The fern 

 frond experimented upon was Athyrium filix faniina, var. 

 Plumosiim etegaus, which was laid flat upon the soil 

 about three years ago, covered with a sheet of glass. 

 The young ferns were now showing themselves, having 

 sprung from the veins of the old frond so laid down. 



Mr. Whitelegge, of Sydney, sent a specimen of a hand- 

 some moss, Spiriden mnelteri, in fruit, which he had 

 collected during a recent scientific expedition to Lord 

 Howes Island. It is a large moss, growing from 

 eighteen inches to two feet long. 



EDINBURGH AND GLASGOW GEOLOGICAL 

 SOCIETIES. 

 These societies had a joint excursion on Saturday to 

 the Camps limestone quarries and the mineral oil works 

 at Oakbank, in the vicinity of Mid-Calder. The quarries 

 were first visited. The rock quarried forms the outcrop 

 of a basin-shaped deposit of very finely-banded limestone, 

 the works following the dip at a pretty sharp angle. A 

 roof eight feet thick, forming the upper layer of the bed, 

 and lying under a tough glacial till, has been left by the 

 workmen, along with massive columns at intervals of 

 about twenty feet; and on entering the cavernous 

 penetralia one is strongly reminded of the ancient temple 

 excavations found in Mesopotamia and Armenia. The 

 oldest and deepest quarry could not be entered : it has 

 been unworked for some time, and has filled with water ; 



