41S NEW YORK STATE MUSEUM 



One qualification, perhaps, needs to be added; namely, that petro- 

 leum as stored in the rocks may be transformed there into the 

 inflammable gas that belongs in the same chemical series and 

 which may be even more stable than the oil, by as much as it is 

 simpler in composition. It may even be that the oil would be 

 entirely converted into gas in the process of the ages. 



It seems altogether probable that the oil and gas which we 

 find in the rocks are of widely different ages, corresponding to 

 the ages of the formations in which they are stored. Thus we 

 may have Cambrian, Ordovician, Silurian, Devonian, Carbonifer- 

 ous, Triassic, Jurassic, Cretaceous and Tertiary petroleums. 



The facts of geology seem to show that it is exceedingly im- 

 probable that gas or oil have been transferred in a large way 

 from one formation to another in the geologic column. This 

 statement requires qualification. That there has been some 

 transfer of petroleum and gas in the rocks is beyond question. 

 They are associated with water and gravitation will always raise 

 them to the highest point in the stratum in which they happen 

 to be. If the reservoir was fractured at the summit of an arch 

 these mobile substances will follow the lines of escape to the 

 surface, if the latter extend thus far, and must certainly diffuse 

 themselves through any porous beds which the fracture crosses. 



With such escapes of oil and gas we are familiar. We call 

 them "surface indications" and they often lead us directly to 

 the storehouse from which they have issued. 



In like manner a porous rock is often found stored with petro- 

 liferous products evidently derived from a stratum or bed directly 

 underlying it. The most common form of such occurrence is a 

 sandstone overlying a carbonaceous shale. When such a series 

 rises to the surface the porous rock is often charged with maltha, 

 resulting from the oxidation of the original petroleum. If the 

 sandstone is in demand for building purposes, the tar is often 

 found exuding from it, even for years. Tar springs, so called, 

 have a like origin, the escaping water of the porous rock carry- 

 ing out some of the inspissated petroleum. 



