TETROLOGY. 205 



Ashes, with some comparative analyses. Journ. Chem. Soc. ser. 



2, vol. xii. pp. 325-331. 

 Contains analyses of average samples of the whole thickness of the 

 main-seam coal at the Sydney Mines, and of that of the Lingan Mine 

 coal, as well as of the ashes of these coals. F. W. R. 



HuDLESTON, W. H. Analyses of Gault, Ironstone, Phosphatic No- 

 dule, and Marl, in paper by F. G. H. Peice. See p. 31. 



Hull, Praf. Edward. Microscopic Structure of Irish Granites. 

 Journ. Roy. Geol. Soc. Ireland, ser. 2, vol. iv. pt. 1, pp. 4-8 

 (plate). 



No. 2. Granite of AUemore, Mayo. — This forms an isolated mass, 

 S. of Louisburg: it is fine-grained, greyish, and consists of quartz, 

 orthoclase, triclinic felspar (? oligoclase), and dark green mica. In 

 places it takes the appearance of graphic granite. It is surrounded by 

 metamorphosed schistose beds, probably L. Silurian, and is older than 

 the U. Llandovery Beds to the S. The orthoclase sometimes exhibits a 

 cross-banded structure. The oligoclase (?) is not often crystalline. 

 The silica is without crystalline form and highly cellular, containing 

 fluid bubbles, sometimes of very irregular form. From the space they 

 occupy it might be inferred that the original vapour was not highly 

 rarefied. Tubes and trichites are rare. The mica shows a wavy struc- 

 ture, and sometimes encloses grains of magnetite, which are also found 

 in the felspar. No. 3. Granite of Ballylcnoclcan, Go. WicMow. — This 

 is considered the best building-stone near Dublin. The author quotes 

 analyses, from which the presence of a soda-felspar had been inferred : 

 this the microscope now reveals. The rock is finely crystaUine-granu- 

 lar, and contains the following minerals — silica, orthoclase, triclinic 

 felspar, grey mica, and mica of a fine bronze colour. The silica is 

 amorphous and contains cells with fluid-bubbles, stone-cavities, trichites, 

 tubes or tracks of gas-bubbles, and gas-cavities (?). The orthoclase is 

 generally subcrystalline, and presents the cross-banded structure, 

 while the triclinic felspar is considered to be albite. E. T. H. 



. On the Microscopic Structure of the Lambay Porphyry (or 



Porphyrite). Journ. Roy. Geol. Soc. Ireland, ser. 2, vol. iv. pt. 1, 

 pp. 44-48, 3 woodcuts ; and Geol. Mag. dec. 2, vol. i. pp. 449- 

 453, 4 woodcuts. 

 The rock is a beautiful ornamental stone, resembling the green por- 

 phyry of Sparta and Marathon in appearance, but quite distinct in 

 mineralogical composition. It has been intruded amongst the Silurian 

 rocks before the Old-Rcd-Sandstone period. The normal rock consists 

 of a dark green base, enclosing pale green crystals of orthoclase, up to 

 aiU inch in length, with cavities containing segregations of chalcedony, 

 cpidote, chlorite, and calcito in vesicular cells. The rock has been 

 considered hornblendic ; but specimens fail under the microscope to 

 reveal this mineral, and show that the dark colouring-matter of the 

 base is duo to the minute crystalline grains of magnetite with a little 



