116 



B. K. EMERSON — -PLUMOSE DIABASE AND PALAGONITE 



If we compare the two differentiates with the normal diabase we see 

 that some CaO, MgO, and Si0 2 would be left over if the diabase split 

 into the two extremes, so that it is perhaps not necessary to derive the 

 quartz and oxides from without. It would suffice if water and carbon 

 dioxide were brought in from without. While I have little doubt that 

 in this case the foreign materials were brought in as I have described — 

 that is, as a calcareous mud — since they are found in the immediately 

 adjacent brecciated area, though not in the same slides with the glass, it 

 would perhaps furnish a better general explanation of the presence of 

 these two substances if we accept the remarkable conclusion of Professor 

 Edward Suess * that there is an abundant and frequent present contribu- 

 tion from the deep-seated molten magma of these and other volatile sub- 

 stances. Then we may imagine that, the C0 2 taking part of the Mg and 

 Ca of the magma locally, the immediately surrounding portions of the 

 magma separated into albite and basic glass, rejecting the excess of Si0 2 , 

 while an inch away from the glass clots the normal conditions remained 

 unaffected and a normal diabase resulted. 



Indeed the enormous quantity of the highly hydrated palagonite pres- 

 ent in many places where basic rocks are abundant, together with the 

 great amount of water that is coming up from the interior through open 

 craters, prompts the suggestion that the deep magma may be or may have 

 been much more hydrated than we are accustomed to assume, and that 

 this hydrated magma may have now and again been erupted, and in by 

 far the greater number of cases explosively erupted ; hence the general 

 ocurrence of the palagonite as a tuff (see page 121). 



In the quantitative classification all the analyses of the Triassic diabase 

 are referred by Professor Iddings to class III, order 5, rang 4 : Auvergase, 

 subrang 3 : Auvergnose. The diabase pitchstone is placed in the next 

 higher subrang, 2 under Auvergnase, showing the slight chemical differ- 

 ence between it and the normal diabase.f The diabase of Middlefield, 

 Connecticut, is referred by Washington to rang 3 : Camptonose, subrang 

 4 : Camptonose J under the same order. The palagonite, assuming it to 

 consolidate into an anhydrous rock, goes under the same class III into 

 order 3: Atlantare and into an unoccupied place, rang 3, subrang 1. 

 The quartz and glass-bearing diabase (analysis IV) goes into class 1 1 : 

 Dosalane, order 4 : Tonalose, and subrang 3 : Hartzase. 



♦Ueber heisse Quellen. Verhand. Gesell. Deutsche Naturforseher und Artze," 1892, p. 3. 



t Chemical Composition of Igneous Rocks. Professional paper no. 18, U. S. Geol. Survey, 1903, 

 p. 49. 



X H. S. Washington : Chemical Analyses of Igneous Rocks. Professional paper no. 14, U. S. 

 Geol. Survey, 1903, p. 819. The same analysis is also cited under the next higher subrang as from 

 Meriden, p. 317. 



