FENNER, THE WATCHUNG BASALT 119 



with the anorthite molecule of plagioclase or with the essential molecule 

 of laumontite and a second with the albite molecule, except at transition 

 points, which, in the present case, are of little importance. 



It is possible that there are other limiting conditions which are more 

 obscure or regarding which present knowledge is insufficient. The evi- 

 dent relations, however, make clear the fact that not more than three of 

 the feldspathoid minerals could exist together in stable equilibrium, and 

 with several combinations not more than two could coexist. 



It is necessary, however, to keep in mind the fact that, even under 

 unstable conditions, solution may be so slow that portions of the mineral 

 or even perfect crystals may persist through a prolonged period. There 

 are indications that certain minerals formed during the first stages of 

 recrystallization disappeared utterly and their nature can only be guessed 

 at, but with the great majority of species, portions have survived through- 

 out. 



In applying the phase rule to the problem, the author does not wish to 

 imply that he believes that a case of this kind is capable of treatment 

 with a high degree of mathematical rigidity. The nature of the case 

 renders this impossible. Each of the minerals present in addition to the 

 feldspathoid compounds introduces an element of uncertainty which can- 

 not be taken into account. It is believed, however, that these effects were 

 rather feeble except with boric acid, which has been considered, and that, 

 using some broadness of interpretation, the deductions of the phase rule 

 are applicable. 



The general results which should be expected are that the minerals 

 formed from various combinations of soda, lime, alumina, silica and 

 water should present a series in which one mineral after another will be 

 found to have been deposited, to have survived through a certain period 

 of stability, and then, with progressively changing conditions, to have 

 passed again into solution, to be redeposited in new combinations. Re- 

 garding the order in which various species should appear, the phase rule 

 affords no information. The tracing out of the sequence will form a 

 chief feature of the petrographic portion of the present paper. 



Without enlarging here upon the evidence which will be presented, it 

 may be stated that the general inferences and conclusions drawn from the 

 application of the phase rule appear to be fully warranted. Careful ex- 

 amination of hand specimens gives additional confirmation. Numerous 

 examples have been collected which afford proof of the instability and 

 breaking down and even the total removal of minerals. Sucli proofs are 

 the etclied and rounded surfaces of crystals, the development of porosity 

 and driisy openings and finally the "negative pseudomorphs," or cavities 



