114 SOURCE OF THE BITUMEN. 



It is idle to speculate on the ultimate source of the asphaltum. The generally attributed 

 source, namely, a deposit of fossil vegetable matter, overheated by volcanic rock, does not 

 occur here apparently. The strata through which it escaj^es are, where observed, almost 

 destitute of vegetable matter ; the brown sandstone wholly, and the greenish having a few 

 traces of fucoids scattered sparingly throughout their structure. The tertiary rocks are in 

 contact with the granite. The sedimentary strata are but a few hundred feet thick before primary 

 rock is met with. There are no palasozoic strata, no extensive beds of metamorphic shale, no car- 

 boniferous strata, to fall back upon to hypothecate its formation. There are no excessive fish 

 remains whose decomposition could be supposed, even by a chemical imagination, capable of 

 producing this mineral. 



Illustrations of the relation of asphaltic effusions to the contiguous strata are given in plate 1, 

 figure 2, plate 4, figures 3, 4, and 6, and plate 5, figures 2 and 3. 



