This composition is such as would result from a mixture 

 of stilbite and laumontite, and although the latter mineral 

 could not be positively identified in the sand examined with 

 the microscope, there seems to be no good ground for doubt- 

 ing that it is actually present. 



It seems remarkable that the material from two different 

 cavities should contain the two minerals in so nearly the same 

 proportions, as indicated by the analyses. 



Concerning the reddish spherules, no data of importance 

 could be obtained except by chemical analysis. Under e above 

 is given the composition found for this substance in material 

 which was apparently very pure. 



The oxygen ratio for this, is : 



RO : R,0 3 : SiO, : H 2 



These figures agree so well with those- obtained for the 

 thomsoDite of the first series (see Analysis I in June number, 

 this Journal), viz : 



that in absence of anything to the contrary, the identity of 

 the two substances can scarcely be doubted. It was noticed 

 here as in the other thomsonite, that about 2 per cent of the 

 water could be expelled only at a very high temperature. 



Thomsonite in the form of these reddish spherules has been 

 deposited locally in great abundance in im-ular cavities on 

 the upper surface of the lower sheet of basalt, and also in the 

 ongular spaces, formed w\\^i\> the scoriaceous crust of the flow 

 has been broken or crumpled. It is here deposited alone, free 

 from stilbite and laumontite, but the spherules are exactly sim- 

 ilar in size and appearance to those formed in the cavities 

 below. 



The ferric oxide in all these minerals seems to replace a 

 portion of the alumina. 



The occurrence of cavities containing these stratified de- 

 posits side by side with those entirely free from anything of 

 the kind is very interesting. It seems to be explainable with 

 plausibility on the theory that fissures formerly led into those 

 cavities containing the reddish deposits, winch' were naturally 

 followed by percolating waters. 



The formation of zeolites in all cavities alike could only 

 begin after the filling up of these fissures by the deposition of 

 mineral matter. In support of this theory, it was noticed that 



