336 DR. J. A. SMYTHE ON 



treated had all the same density, except when attached to 

 small particles of the much decomposed basalt. The analysis 

 is given in Table A, No. I., and, for comparison, the analysis 

 of the felspar inclusions from the Crookdene and Collywell 

 Dykes (Nos. II. and III. These are quoted from Heslop and 

 Smythe's paper, "The Dyke at Crookdene," p. 7). 



Table A. Analyses of felspar inclusions from Hartley (I.), Crookdene 

 (II.) and Collywell (III.) Dykes. 





I. 



II. 



III. 



SiOo 



4577 



45-88 



46-61 



A1 3 3 



34-20 



34'3i 



35'i3 



Ti0 2 



trace 



0-04 



0-13 



Fe 2 3 



o73 



0-83 



0-25 



CaO 



18-52 



18-28 



16-74 



MgO • 



none 



none 



none 



K 2 



0'12 



O-II 



0-15 



Na>0 



1-04 



0-82 



1-05 



H 2 



25 



0-14 



- 22 



10063 100-41 100-28 



The felspar is thus nearly pure anorthite, CaO, A1 2 3 , 2Si0 2 

 (calculated, CaO=2o - o9, Al 2 O s =36*66, Si0 2 =43'25) and, 

 while closely allied to the Collywell inclusion, agrees in com- 

 position down to the minutest detail with the felspar of the 

 Crookdene Dyke, 24 miles away. If the soda present be 

 taken as a measure of some admixture with albite, Na 2 0, 

 A1 2 3 , 6Si0 2 , or Na AlSi 3 8 (=Ab) and the lime as due to 

 the main constituent, anorthite (= An), then the mineral should 

 contain 8 per cent, of the former and 92 per cent, of the latter, 

 and, in fact, the analysis agrees with that calculated for a rock 

 so constituted (represented by the symbol Ab : , An n ) as is 

 seen from Table B. 



Table B. I. Analysis of inclusion from Hartley Dyke. II. Com- 

 position calculated for a mixture of 8 per cent, albite and 92 per cent, 

 anorthite (Abi, Ann). 





I. 



II. 



Si0 2 



4577 



45 '34 



Aloos 



34-20 



35'23 



CaO 



18-52 



18-49 



Na 2 



1-04 



0-94 



If the ferric oxide in the Hartley rock (0-73 per cent.) be 

 regarded as replacing alumina, the agreement is still better, 



