110 A^'NAL8 NEW YORK ACADEMY OF SCIENCES 



bands and circular markings, suggesting in form the spherulites and 

 similar features found frequently in the glasses. The resemblance to the 

 chloritic nodules of fig. 2 and other sketches is obvious, and their occur- 

 rence in the present case is ascribed to a persistence of the spherulitic 

 structure during recrystallization, the effects being preserved by an in- 

 soluble dust of TiOj or MnOo. Xext to these crusts lies a narrow band 

 in which the basaltic texture appears, but in finely crystalline develop- 

 ment, and this is believed to mark the transition from glass to normal 

 basalt in the original rock. Beyond this the texture is that of ordinary 

 basalt. Recrystallization has been complete in the glass, except for the 

 insoluble inclusions. In the finely crystalline border and in the normal 

 facies of the rock, it has made sufficient advance to change the labradorite 

 and diopside to prehnite and albite for a short distance without mucti 

 disturbance of the texture. A little further, and both the texture and 

 mineralogic composition are almost unchanged. Similar phenomena, 

 showing that alteration was checked when the crystalline portion of the 

 basalt was reached, are seen in several slides. 



The fact that circulation was comparatively rapid had important 

 results in the nature of the secondary minerals. Under these conditions, 

 rapidity of solution or time taken for a mineral to form a solution of a 

 certain strength, considered apart from total solubility or quantity present 

 in a saturated solution, affects the nature of the changes which take place. 

 When water is at rest in the interstitial spaces in a rock, a mineral which 

 dissolves slowly may nevertheless reach a comparatively large total solu- 

 bility, but if the water moves along channels of circulation, the amount 

 of a slowly soluble substance which is taken up may never reach the 

 amount necessary to carry forward sufficiently those reactions by which 

 new minerals of less solululity containing its elements are deposited, and 

 whatever amount goes into solution is removed altogether. 



In the original basalt, magnesia and the oxides of iron reach a large 

 percentage, being principal constituents of the diopside and magnetite. 

 In the later minerals, the proportion of iron and magnesia is insignificant. 

 In places, large masses of zeolitic minerals and calcite are found from 

 which all compounds containing iron and magnesia have been removed. 



Another effect of the circulation of the waters is that the substances 

 dissolved are distributed through the solution, and new products may 

 crystallize at a distance from those from which their elements were de- 

 rived. With standing, interstitial water diffusion of dissolved substances 

 can only occur through the slow action of osmotic pressure. Conse- 

 quently, under the latter circumstances, the new minerals are much more 

 apt to show intimate association with the old and little tendency to mi- 



