88 Prof. Johnston on the Composition of certain 



The small defect of carbon and excess of hydrogen in the 

 analysis are both on the side in which they ought to appear 

 when experimental results are compared with an accurate 

 formula. 



This resin therefore presents another example of the con- 

 nexion of resinous substances with oil of turpentine C40 H32; 

 and if the rational formula C^oHgj + O be the true one, it ex- 

 hibits the lowest state of oxidation of this radical with which we 

 are yet acquainted. It is very slightly acted on by alcohol, 

 but the solution gives a white precipitate with an alcohoHc 

 solution of acetate of lead. It is either altogether an acid 

 resin therefore, or it contains a small quantity of a more solu- 

 ble resin which is so. 



VII. Ilcsinfrom Settling Stones. 



In Brewster's Edinburgh Journal of Science, N.S., vol. iv. 

 p. 122, I described as a new variety of mineral resin^ a sub- 

 stance I had met with among the old heaps of a lead-mine 

 in Northumberland known by the name of Settling Stones, 

 the working of which has been recently resumed. This mine 

 is situated at the point of junction of a number of intersecting 

 faults and veins, along which the strata are thrown up and 

 down in various directions. By one of these faults the great 

 whin sill of that district is brought to day, and forms an 

 escarpment over which the waters of a little rivulet descend 

 from a height of 20 or 30 feet. Near the veins the trap is 

 much impregnated with lime, and the cheeks or walls of 

 the vein are sometimes almost a perfect limestone, and have a 

 gray or bluish gray colour. It is on these walls of the vein, 

 resting on and occasionally covered by calc spar, brown spar, 

 or pearl spar, that the resinous substance occurs. It is in the 

 form of drops or flattened portions, more or less rounded, as 

 if it had once been in a fluid or softened state. It is hard, 

 brittle under the hammer, but exceedingly difficult to reduce 

 to fine powder in the mortar : even after long rubbing the 

 angular fragments can still be recognised. Its colour varies 

 from pale yellow to deep red, its specific gravity from ri6 

 to I'S*, and it exhibits a pale green opalescence. It does 

 not melt at 400° Fahr., but it burns in the flame of a candle, 

 and gives empyreumatic products when fused in a close tube 

 over a spirit-lamp. It is insoluble in water and is very slightly 

 acted upon by alcohol. 



Having a small quantity of this resinous substance at my 

 disposal I availed myself of the opportunity of determining 

 its composition, with the view of comparing it with that of 

 the fossil copal above analysed. In external appearance they 



