Mr Meikle on the Electricity, fyc. of Steam. 55 



presence by their colouring properties, and their discovery is 

 not attended with great difficulties. 



Lead-glance and calamine are chiefly found in one and the 

 same kind of repositories in limestone ; and, of the occurrence 

 of copper-ores in the secondary rocks, the copper-slate of Thu- 

 ringia and Mansfeld is the most remarkable and the most in- 

 teresting example. 



In this short summary of the secondary rocks in relation to 

 their repositories of useful minerals, I must, in conclusion, add 

 the remark, that these rocks enter, for considerable distances, 

 the valleys of the primitive and transition rocks, which extend 

 to the plains, and that rocks of the same kind not unfrequently 

 occur in places which are not in actual connection with the 

 plains. Such places, as well as the generally wide valleys, are 

 in this respect to be viewed as small plains, or isolated groups 

 of secondary rocks, whose small dimensions facilitate exceed- 

 ingly the search for repositories of useful minerals ; a search 

 which requires no particular directions. 



It is not necessary to treat particularly in this place of the 

 alluvial and tertiary formations, because those of them which 

 appear as solid rocks are to be treated and investigated like 

 the secondary series, and those which occur as loose incohe- 

 rent masses are at the surface, and therefore require no par- 

 ticular preparation for their discovery. 



On the Electricity and Explosive Force of Steam, and on the 

 Economy of the Hot-blast Furnace. By Henry Meikle, 

 Esq. Communicated by the Author. 



Much curiosity has lately been excited by the electrical 

 phenomenon observed in the condensation of the steam which 

 escaped from a high-pressure boiler at Cramlington Colliery, 

 near Newcastle, and which was briefly this : The engine-man, 

 when happening to be standing where the steam, issuing from 

 a leaky joint, was condensing into a cloud about his legs, put his 

 hand to the lever of the safety-valve, and instantly experienced 

 an electrical shock. Scientific men, on examining this phenome- 

 non, as detailed in the Philosophical Magazine for November last, 



