208 PETROLOGY. 



but the enclosures undergo no change. It becomes vesicular when 

 heated to near its fusing-point. F. W. R. 



Knop, a. Ueber Kieselsaure-Abscheidungen und Oolithbildung.. 

 [Separation of Silica, and formation of Oolite.] N. Jahrb. Heft 3, 

 pp. 281-288, woodcut. 



Discusses the conditions under which silica can separate in the 

 various forms of quartz, tridymite, asmanite, and opal. Describes a 

 hornstone of oolitic structure occurring in the Trias of the Upper Rhine 

 country. Reviews the hypotheses advanced to account for the formation 

 of oolites in general, and records observations tending to show that they 

 may occasionally be formed by incrustation of bubbles of gas liberated 

 in calcareous waters, or by deposits in small shells. F. W. R. 



Lasaulx, Dr. A. von. Ueber sogenannte Hemithrene und einige 



andere Gesteine aus dem Gneiss- Granitplateau des Departement 



Puy-de-D6me. [So-called Hemitrene &c. from Puy-de-Dome.] 



N. Jahrb. Heft 3, pp. 230-260. 



Concludes, from microscopic and chemical examination of typical 



examples of " Hemitrene," that this name should be abolished, as it is 



at present applied to several rocks essentially distinct, and having 



nothing in common except the presence of carbonate of lime. Also 



describes diorites, porphyries, and other rocks, from the plateau of 



gneiss and granite in the Dep. of the Puy-de-D6me. F. W. R. 



— . Sopra le rocce eruttive del Yicentino. [Eruptive rocks 

 of the Yicenza district.] Boll. R. Com. geol. Ital. pp. 16-30. 



An Italian translation of part of a paper in the Zeitsch. deutsch. 

 geol. Gesell. Bd. xxv. (1873). Contains descriptions and analyses of 

 various porphyrites, pitchstone-porphyry, trachytes, gabbro, &c. from 

 the Yicenza district. E. B. T. 



Lee, John E. Notes on Trappean Rock. Trans. Devon. Assoc, 

 vol. vi. part 2, pp. 400-411. 4 plates. 



This paper is illustrated by a series of 24 sketches, principally taken 

 in Ireland, Scotland, France, Germany, and Italy, all relating to the 

 structure of trap, basalt, and volcanic rocks. The author first describes 

 the general peculiarities of basalt and trap, such as the varieties of the 

 prismatic form, with the cross and cup sections of the prisms and their 

 tendency to concentric weathering. In the second place is noticed the 

 alteration caused by the intrusion of trap-dykes upon limestone, coal, 

 sandstone, or whatever rock may be in proximity to them. The con- 

 cluding part is a consideration of the effects which trap and volcanic 

 action have upon scenery. T. M. H. 



Leech, Prof. Notice of a Lightning-tube or Fulgurite found near 

 Fayetteville, N. 0. Proc. Ac. Nat. Sci. Philad. p. 145. 



LfivY, Michel. Note sur quelques roches analogues aux porphyres 



