2o6 



THE MUSEUM. 



AKiiOW-lIEADi) (4) 



weeds, but chiefly from marine animals, 

 such as corals, and mollusks. It is 

 well known that petroleum gives off 

 gas freely, especially when heated ;and 

 this is the source of the natural gas 

 now being obtained from the oil fields 

 of Pennsylvania and Ohio. When 

 the conditions are favorable for the 

 escape of this gas its evolution contin- 

 ues, and the petroleum becomes less 

 and less liquid, and finally changes to 

 asphaltum. 



Where this drying up of the petro- 

 leum has taken place in fissures, or 

 cavities in the earth's crust, asphaltic 

 deposits of great purity and value have 



been formed. The brilliant and al- 

 most jet-like albertite in Hillsboro, 

 New Brunswick, which was mined for 

 many years and used for the manu- 

 facture of gas, is a variety of asphal- 

 tum having this origin. The graham- 

 ite of West Virginia is a substance 

 closely resembling albertite, and oc- 

 curs in a similar fissure or crevice. It 

 is quite certain, however, that the 

 typical asphaltum, which is used so 

 extensively for paving, roofing, and 

 like purpose, has not been formed 

 chiefly in this way. It is not of ma- 

 rine or animal origin, for the evidence 

 is very conclusive that, like the coals, 



