201 



PETROLOGY. 



AUport, S. On the Metamorphic Rocks surrounding the Land's End 

 Mass of Granite. Quart. Jouni. Geol. Soc. vol. xxxii. pp. 407- 

 427, pi. xxiii. 



Describes first some of the slates metamorphosed hy contact with 

 granite. These are changed into tourmaline-schist and mica-schist — 

 new minerals, such as quartz, tourmaline, and three varieties of mica, 

 resulting from the metamorphism, with a foliated texture and a concre- 

 tionary action tending to segregate the quartz and mica, and produce a 

 spotted schist. Then describes a number of altered dolerites ; in these 

 the pyroxenic constituent is replaced by actinolite and hornblende, in 

 belonites, blades, and flakes. Many of the altered dolerites exhibit an 

 imperfect cleavage. Calls attention to the possibility of some horn- 

 blende-schists being really altered doleritic rocks or diorites. The 

 granite of Cornwall and Devon is an eruptive, not a metamorphic, rock. 

 There is evidence to show that the Cornish rocks were cleaved and 

 sometimes contorted before the granites were intruded. T. G. B. 



Anon. Excursion to Antrim and Tardree. Proc. Belfast Field Club, 



ser. 2, vol. i. pp. 155-160. 

 Tardree Mountain trachyte-porphyry (Eocene) is coarsely crystalline, 

 grey to white. Crystals of quartz and felspar in felspathic base. 



Berwerth, Dr. Friedrich. Felsarten aus der Gegend von Resign ano 

 und Castellina Maritima siidlich von Pisa. [Rocks from S. of 

 Pisa.] 3Iin. Mitth. Heft iv. pp. 229-240, with woodcut. 



The rocks described are diabase, gabbro, serpentine, and serpentine- 

 rock {Serpentingestein). The last is composed of serpentine, diallage, 

 and magnetite, with microscopic granules of calcite and particles of 

 iron-glance. It may be regarded as a serpentine containing diaUage ; 

 but as the diallage is fresh, and forms from | to 5 of the mass, the 

 author prefers regarding it as a distinct rock. In some specimens the 

 alteration of diallage to serpentine may be traced. No olivine was 

 detected. F. W. R. 



Bonney, Rev. T. G. On Columnar, Fissile, and Spheroidal Structure. 

 Qxai-t. Jotirii. Geol. Soc. vol. xxxii. pp. 140-154. 



After briefly noticing columnar structure, in explanation of which 

 the author accepts the contraction theory, he describes fissile, tabular, 

 curvitabular, cup-and-ball, and spheroidal structure, giving numerous 

 examples. The last is considered in detail, is shown to exist in rocks 

 other than igneous, and to be identical with the perlitic structure of 



