452 Analyses of Books. [Junk, 



MaccuUocli. — Theic forts have been observed ia different parts of 

 the north of Scotland and in Galloway. Nothing is known relative 

 to the time of their erection, or the people by whom they were 

 built. Two opinions have been advanced : that they were vitrified 

 on purpose, and that they were vitriHed by accident. Dr. Mac- 

 cuUocli shows, by an examination of the stones of which they are 

 composed, that the latter opinion cannot be correct. He examined 

 two of these forts : Dun Mac Sniochain, in Argyleshire, and Craig 

 Pliadric, in Inverness-shire. In both the walls consist chiefly of 

 primitive rocks. These have been mixed with a considerable quan- 

 tity of a kind of amygdaloid, which easily fuses, and by the fusion, 

 more or less complete, of this material, the vitrification has been 

 brought about. The amygdaloid differs considerably in its nature at 

 the two forts. At Araworth, in Galloway, there is no amygdaloid ; 

 the rocks are grey-wacke and grey-wacke-slate. Some portions of 

 this grey-wacke are fusible, from a mixture of calcareous spar. 

 Accordingly this fort is only vitrified in a few detached spots. 



IX. On the Suhllmallon of Silica. By Dr. Macculloch. — He 

 had exposed a mixture of the oxides of tin and lead in a crucible 

 covered by another, for some hours, in a furnace at a heat con- 

 jectured to be between 130° and 140° Wedgewood. On cooling, 

 the top of the uppermost crucible contained some small filamentous 

 crystals, white and brilliant, crossing each other in all directions. 

 They were found to be crystals of pure silica. Dr. M. was not able 

 to repeat this experiment with success. 



X. Observations on the Specimens of Hippurites from Sicily, 

 presented to the Geological Socieli/ by the Hon. Henry Grey 

 Bennet. By James Parkinson, M.G. S. — These specimens are so 

 perfect as to enable Mr. Parkinson to determine some things re* 

 specting the original structure of the shells. The supposed oper- 

 culum mentioned by Picot la Pevrouse could not be distinguished. 

 Mr. Parkinson thinks that the hippurites, orthoceratites, ammo- 

 nites, &c. had the means of elevating themselves to the surface of 

 the sea, like the nautilus; and some things which he obierved in 

 these specimens give countenance to this idea. 



(^'u be contimud.) 



Article XI. 



Proceedings of Philosophical Societies. 



ROYAL SOCIKXr. 



On Thursday, jhe 27th of April, a paper by Mr. Seppings wa» 

 read, containing further particulars respecting his improved mode 

 of ship-building. As, immediately after his last paper a paper was 

 read to the Roval Society, containing theoretical objections against u 

 mode of building ships to which in Lis opiyioij theory was not 



