ORIGIN AND USE OF NATURAL GAS AT MANITOU. 25 



may proceed more rapidly in one kind of rock than in another. 

 The application to be made of the foregoing observations 

 depends upon the fact that waters thns hiizldy chartj:ed with 

 mineral matters in rock tissures would be well adapted to 

 produce reactions upon limestones if they should chance to 

 come in contact with them. It should not escape notice that 

 the flow of gas at Manitou takes place within a very limited 

 area, and that no other similar springs are found in this im- 

 mediate region. It is a very local phenomenon. Whatever 

 the causes which give rise to the gas, they can have no gen- 

 eral application to the similar series of rocks extending for 

 many miles along the mountain slopes, else the evidences of 

 their action would be more widely distributed.. Hence some 

 local cause is to be sought at Manitou as the producer of the 

 gas. 



Having thus examined the situation at Manitou and briefly 

 reviewed some theories of the evolution of carbonic acid gas 

 from the earth, it is now possible to more definitely assign a 

 reasonable cause and source of the flow of gas in question. 

 It seems to be generally agreed that the carbonates formed 

 through the decomposition of silicate rocks by atmospheric 

 waters will not bj' any known reactions in those rocks alone 

 account for a large flow of gas. Also the evolution of carbon 

 dioxide by the slow, natural distillation of carbonaceous mat- 

 ters deeply buried in strata, is an explanation not applicable 

 to the present case, because of the great purity of the Manitou 

 gas. The disengagement of the gas from limestones sub- 

 jected to heat from rising isogeotherms appears improbable 

 because the strata at Manitou seems not to be very deeply 

 buried, and because the salts found in the water of the springs 

 point to another class of rocks as a source, and also because 

 the springs are confined to so limited an area. 



The presence of masses of igneus rocks near the limestones 

 may be considered a possible explanation of the phenomenon, 

 since though no such eruptions outcrop near Manitou, there 

 may yet be intrusive masses of them buried more or less 

 deeply beneath the gravel or sedimentary beds. The waters 

 of the sjjrings would probably have a much higher tempera- 

 ture than they now possess if masses of igneus rock retaining 



