84 REPORT — 1860. 



chlorite, epidote, and alumina-garnet, and in those strata where lime and magnesia 

 are absent, chloritoid Andalusite, staurotide, and kyanite. These minerals, which are 

 only formed in aluminous sediments that have lost their alkalies, become more and 

 more abundant on the newer strata. 



The consideration of the composition of mineral springs, as Mr. Hunt has remarked, 

 shows that the solvent action of water removes from sediments chiefly soda, lime, and 

 magnesia, and with the concurrence of organic matter, oxide of iron, so that the more 

 permeable strata, and generally more siliceous, retain scarcely any other bases than 

 alumina and potash ; the argillaceous and less permeable beds, on the contrary, retain 

 the whole of their bases. The operation of processes continually going on in nature 

 therefore tends to divide the silico-argillaceous rocks into two classes, whose meta- 

 morphism and displacement will give rise, on the one hand, to granites and trachytes, 

 and on the other, to rocks made up of basic felspar and pyroxenes. 



The author regards all the so-called igneous rocks as altered and translated sedi- 

 ments, and distinguishes them by the name of exotic rocks, from the same sediments 

 altered in situ, which may be called indigenous plutonic rocks. He insists upon the 

 fact that the chemical composition and, for the most part, the lithological characters 

 of all the varieties of intrusive rocks may be found represented in metamorphosed sedi- 

 ments. 



Mr. Hunt has called attention to the fact, that as long ago as 1834 Keferstein 

 advanced the opinion that all plutonic rocks are only altered sediments, and thus 

 anticipated in part Sir John Herschel's theory of earthquakes and volcanic pheno- 

 mena, to which Mr. Hunt has given a wider extension, connecting it with Mr. Bab- 

 bage's speculations on the result of the rising of the isothermal lines in the earth's 

 crust, consequent upon the accumulation of sediments. The first result of this heat 

 would, as Mr. Babbage has shown, produce expansion and elevation ; but when meta- 

 morphisin takes place, the contraction attendant upon the conversion of the sediments 

 into the denser silicates, such as chloritoid pyroxene, garnet, epidote staurotide, and 

 chiastolite, must produce an effect directly opposite. In this way Mr. Hunt conceives 

 that while the earth's nucleus may be a solid, although incandescent mass of anhydrous 

 silicates, we may suppose that the inferior strata, which are undergoing metamorphism 

 and igneo-aqueous fusion, agreeable to the views of Poulett Scrope, Herschel, Scheerer, 

 and Sorby, are contracting in such a manner, that we may possibly admit with Elie 

 de Beaumont a shrinking of the fluid mass beneath, which will explain the great plica- 

 tions of the earth's crust, and thus reconcile this theory with the view of a solid 

 nucleus. At the same time he is inclined to refer the great movements of elevation 

 and subsidence, for the most part, to what Herschel has described as " the disturbance 

 of the equilibrium of pressure" consequent upon the transfer of sediments, while the 

 yielding mass reposes upon a mass of matter partly solid and partly liquid. 



These views will be found in the ' Reports of the Geological Survey of Canada for 

 1857 and 1858,' where the experiments upon gypsum and magnesian rocks are given 

 in detail. Also in a memoir published in the ' Quarterly Journal of the Geological 

 Society' for Nov. 1859. 



On the Igneous Rocks interstratified tvith the Carboniferous Limestones of the 

 Basin of Limerick. By J. Beete Jukes, M.A., F.R.S. 



The author called attention to some of the lately published sheets of the ' Geological 

 Survey of Ireland,' including this district, and stated that the ground had been sur- 

 veyed by Messrs. Kinahan, Foot, O'Kelly, and Wynne. 



He gave a brief sketch of the physical structure of the country around Limerick, 

 and then proceeded to describe its igneous rocks. These are of two kinds, trap and 

 trappean ash. The trap varies greatly in texture and aspect, more perhaps than in 

 mineral composition. The trappean ash (or tuff) is the result of the mechanical ero- 

 sion of the igneous rock, either during the time of its eruption or immediately after, 

 and before it was buried under other aqueous rocks. It consists of grains or frag- 

 ments of trappean material, varying from the finest powder to a coarse conglomerate, 

 with blocks several inches in diameter, and often contains large and small fragments 

 of limestone, and sometimes of other matters. 



It is perfectly stratified, lying in regular beds, interstratified both with the limestone 



