36 ME. F. EUTLEY ON TFFACEOIJS EHFOLITIC [Feb. I9OI, 



section which exhibit a brown colour in ordinary transmitted 

 Jight the globuhtes are more densely packed, and where these 

 cumulitic aggregates occur we may easily recognize them as portions 

 or the nearly isotropic matrix. 



As already mentioned, the fine streaky markings cut throu^^h both 

 the matrix and the meshes of the altered felspar-fragments, the latter 

 causing no deflection of the streaks. It is, therefore, clear that the 

 streaks cannot be indicative of the fluxion of a lava. The rock may 

 possibly have been a vitreous lava, freighted with a preponderance 

 ot telspathic lapilli and dust. This seems indeed to be the case 

 since the "rock partakes more of the character of a tuff than of 

 a lava. It appears that solfataric action is mainly accountable 

 lor its present condition. 



]^o 3 Dufton Pike.—This specimen was given to me by the 

 late Prof. A. H. Green, F.R.S., and in general appearance so closely 

 resembles the rock last described that it seemed quite likely that it 

 would present the same microscopic characters. This supposition 

 is tully borne out by an examination of the section ; therefore the 

 foregoing- description of m. 2 applies equally well to No. 3, except 

 that m the latter the fragments are somewhat less densely packed 

 save along a few irregular lines. ' 



The following are Mr. Philip Holland's analyses :— 

 An-alyses of Rocks fbom DuFioiir Pike. 



I. II. 



Per cent. Per cent 



SiO^ 69-00 71-05 



1-150 1-134 



TiO, -45 .47 



^A 16-88 15-30 



•16-5 -15^ 



y ^^2^3 -88 .70 



•005 .004 



^'^ - -66 



-009 



^^^ not sought trace 



CaO 1-04 -29 



•019 -005 



^aO not sought '11 



MgO 02 -25 



^P 3-88 6-18 



l^asO 4-64 0.24 



CO/. Combined water, ] *^'^ '052 



and matter not deter- i 3-21 i-an 



mined J ^ ^-^ 



* Carbon-dioxide was detected in both rocks, and, for equal weights of ih. 

 powdered rock, the effervesceuce noticeable on moistening with hvdrofh W:/ a 

 was much more marked in Jfo. I than in No II The%m«ll Y'^^^^^^^^^^ ^eid 

 the molecular ratios for the percentages beneath wh^chth'yire^;:^^^^^^^ 



