1897.J XATURE AXD ORIGIN" OF PETROLEUM. 105 



gaseous, often depends upon the temperature at which they are at 



the moment when they are observed Petroleum becomes 



solid when it has lost its light oils by exposure. They designate 

 as asphalte a calcareous rock impregnated with bitumen, whilst if it 

 be mixed with sand or gravel they apply the term petroleum " 



(P- 113)- 



''In presence of this uncertainty, it has appeared to me prefer- 

 able to proceed to the study of the deposits by groups, and to adopt 

 thus a purely methodical system. 



'' To this end I have established the four following groups : 



'* I. The asphaltic and bituminous deposits. 



''2. The bituminous schists. 



'' 3. The petroliferous and bituminous deposits. 



" 4. The natural combustible gas." 



He then proceeds to discuss the subject along these inadequate 

 and purely artificial lines, which time will not permit me to analyze 

 in detail. It is sufficient for my purpose to say, that he concludes 

 that bitumens have been produced in every case by a special decom- 

 position of animal matter at the points where they are now found. 



He thinks that because the bituminous limestones of Seyssel and 

 Val de Travers are intercalated between beds of barren rock that 

 the bitumen must have been formed i7i situ. That is by no means 

 a necessary conclusion. The bitumen in a state of vapor, and 

 probably accompanied by steam, expanded into the porous beds 

 laterally, while passing through fissures in the compact and barren 

 beds. When the Seyssel rock has been exhausted of its bitumen 

 by chloroform and is examined under a microscope, it is found to 

 be an amorphous mass of coarse-grained chalk with the finest parti- 

 cles one ten thousandth to one twenty thousandth of an inch in 

 thickness — so fine that they pass through fine filter paper. 



Any one familiar with the sea-shore has found shells of the com- 

 mon clam {cardtiivi) filled with sand and saturated with the pro- 

 ducts of the decomposition of the soft parts of the bivalve dissolved 

 in water. It is not an infrequent occurrence in regions where bitu- 

 men is abundant upon sea-coasts to find the shells of such bivalves 

 filled with sand saturated with bitumen. The carbon contained in 

 the solid or semi-solid bitumen required to saturate the dry sand 

 that fills such shells is many times that found in the dried soft parts 

 of the animal that occupied the shell. Such shells are common on 

 and near the coasts of southern California. T^I. Jaccard calls atten- 



