1823.] Scieniifid Intelligence. 165 



which passes into serpentine, in which form it continues through 

 a great part of its course ; it lies parallel with the strata. The 

 lower red sandstone, which is for the most part schistose, and 

 not of great thickness, alternates with greywacke at its juncture, 

 and the greywacke with argillaceous schist. A large mass of 

 porphyry resembling that of the elvans of Cornwall, intersects in 

 one part of the district the superior beds of the greywacke form- 

 ation. The paper concludes with some observations on the 

 primary rocks of the Grampians in the county of Forfar. 



June 20. — The following papers were read : 



A Notice on some Fossil Bones of an Icthyosaurus from the 

 Lias near Bristol ; also on two new Species of Fossil Teeth. By 

 George Cumberland, Esq. Hon. Mem. GS. 



A Letter accompanying some Specimens from Stonehenge. 

 By Godfrey Higgins, Esq. 



An Extract of a Letter from Lieut. J. Short, RE. addressed 

 to, and communicated by. Dr. Babington, PreSi GS. containing 

 some remarks on the Isle of Bourbon. 



The Isle of Bourbon, which is situated about 120 miles from 

 the Mauritius, and is 150 miles in circumference, appears to be 

 chiefly of volcanic composition. An active volcano still exists. 

 Although beneath the tropics, perpetual snow and ice cover the 

 summits of some of the mountains which rise to an elevation of 

 10,000 feet. Lieut. Short observed basaltic columns of great 

 height exposed in some parts of the island, and found ohvine, 

 lava, zeolite, and puzzolana, abounding throughout the rocks. 



A Notice respecting the Pebbles in the Bed of Clay which 

 covers the new red Sandstone in the SW of Lancashire. By 

 John Bostock, MD. VPGS. 



Article XII. 



I SCIENTIFIC INTELLlGliNCE, AND NOTICES OF SUBJECTS 



: CONNECTED WITH SCIENCE. 



I. Dr, Wollaston^s Method of detecting Magnesia^ on the smallest Scale, 



Dissolve in a watch-glass, at a gentle heat, a minute fragment of 

 the mineral suspected to contain magnesia, dolomite for example, in a 

 few drops of dilute muriatic acid ; to this solution, add oxalic acid, to 

 render the lime that may be present insoluble ; then pour in a few 

 drops of a solution of phosphate of ammonia or soda. Allow the pre- 

 cipitate to settle for a few seconds, and decant a drop or two of the 

 supernatant clear liquid on a slip of window-glass; on mixing with this 

 liquid two or three drops of a solution of the scentless carbonate of 

 ammonia, an effervescence takes place; draw off to one side with a 

 glass rod, a little of the clear solution, and trace across it, with the 

 pressure of a point of glass or platina, any lines or letters on the glass 

 plane; on exposing this to the gentlest possible heat (as making a little 



