700 iiEPOKT— 1887. 



2. On the PhylUtes of the Isle of Man. 

 By Professor W. Boyd Dawkins, F.E.S. 



Professor Boyd Dawkins called attention to the slates of the Isle of Man^ which 

 present every gradation from the ordinary slate with minute crystals of mica, 

 deposited in the planes of cleavage, to a twisted and highly altered rock, Phyllite, 

 containing so much mica as to appear silky. This has been subjected to second- 

 ary cleavage (slip-cleavage of Bonuey), which has resuifcd from a pressure 

 which has broken through the original lines of cleavage. Wherever in the 

 original slate a quartz vein has occurred, the friction between it and the softer 

 Phyllite when the pressure was applied has caused the development of large flakes 

 of mica, and in some eases of a tibrous hornblendic material. Both these are due 

 to the local development of heat. 



3. On ThinoUte and Jarrowite. By Professor G. A. LiEBOCr, M.A., F.G.S. 



The thinollte of Clarence King, from 'Lake Lahontau,' in Nevada, recently 

 described by E. S, Dana ('Zeit. Kryst. Min.' Bd. xi. p. 285, and ' Bull. U. S. Geol. 

 Survey,' vol. ii. No. 12), is regarded by the author as the same mineral species as 

 Jarrowite, long since recorded from the alluvial beds of the river Tyne at Jarrow. 



4. A Shropslvire Picrite. By W. W. Watts, 3LA., F.G.S. 



Tn this paper the author described a variety of picrite which occurs in the 

 Shelve and Corndon district of Shropshire. The rock has an opliitic structure, 

 and contains olivine grains set in large plates of brownish augite A certain 

 amount of plagioclase and magnetite are present, together with a smaller quantity 

 of brown mica. The largest dike runs N.E. and S.W, from North Dysgwylfa 

 farm to Shelve pool, but blocks of it are found widely scattered through the region, 

 so that it is perhaps plentiful in the district. This dike crosses the direction of the 

 intrusive andesites and dolerites described in the ' British Association Report for 

 1886,' and is the latest intrusion, so that it must be at. least post-Silurian in age. 

 It is sharply marked off' from the other intrusive rocks by the abundance of olivine, 

 a mineral scarce in, if not absent from, the other intrusive rocks. Such a well- 

 marked rock type will be useful to those studying the Shropshire erratic blocks. 



5. On the Mmeralogical Constitution of Galcareoxoi Oryanisms. 

 By Yaughan Cornish and Percy F. Kendall. 



Introduction. — In Dr. Sorby's presidential address to the Geological Society 

 in 1879 it was stated that both Calcite and Aragonite occur in organic structures, 

 and that Aragonite fossils are less stable than those of Calcite. 



It appeared probable that carbonic acid has been the agent which effected the 

 removal of the Aragonite, but we had found no published experimental data to show 

 that it would remove Aragonite more readily than Calcite. 



Part I. — An account of the experimental evidence obtained as the cause of the 

 inferior stability of Aragonite fossils as compared with those formed of Calcite, with 

 observations on the geological conditions favourable to the removal of Aragonite 

 fossils. 



It was pointed out by one of us ^ that those shells classed by Dr. Sorby as 

 Calcite are characterised in the fossil state by a compact texture^nd by translucency, 

 while the Aragonite shells are opaque and of a chalky appearance. 



Exyeriment 1. — A Calcite and an Aragonite shell of about equal weight and 

 surface were subjected to the action of carbonated water and then weighed. 



Result. — The Aragonite shell lost between two and three times as much in pro- 

 portion to its weight as did the Calcite shell, and it fell to pieces. 



Experiments 2 and 3 were made upon finely liowdered Calcite and Aragonite. 



' Geol. May. Nov. 1883. 



