452 Dr. Heddle on Table Spar from the Morne Mountains. 



3. The periods of the horizontal and vertical components, fol- 

 lowing the law of the geographical latitude, and occurring at 

 hours wholly different from the variations of temperature, show 

 a different origin from these. Therefore, if the coincidence in 

 time, in the variations of the temperature and declination, have 

 contributed to the belief of the existence between these two of a 

 mutual relation of cause and effect, the study of the other com- 

 ponents makes this coincidence disappear, and therefore destroys 

 every foundation of the hypothesis. 



4. All the phenomena hitherto known of the diurnal mag- 

 netic variations may be explained by supposing that the sun 

 acts upon the earth as a very powerful magnet at a great 

 distance. 



LXII. On Table Spar from the Morne Mountains. 

 By Dr. M. Forster Heddle*. 



HAVING by my analysis of the Edinburgh Castle Rock 

 pectolite taken table spar out of the list of British mine- 

 rals, I have more than usual pleasure in reintroducing it from 

 the Morne Mountains. 



Two analyses were made ; the first on a specimen sent me by 

 Mr. Greg, the second on one obtained from an Irish dealer, with 

 the following results : — 



On 25 grs. On 30 grs. 



Silica .... 51-360 50-434 



Oxide of iron . -980 -840 



Lime .... 4.2-500 43-920 



Magnesia . . -484 -390 



Water . . . 1480 1-360 



Carbonic acid . not det. 2*371 



99-321 



The powdered mineral absorbs "142 per cent, of moisture, and 

 before the blowpipe gives slight and but momentary evidences of 

 the presence of soda. 



Both of the above specimens are contaminated by an admix- 

 ture of carbonate of lime, doubtless derived from the matrix, 

 which is limestone altered by heat. 



The table spar from this locality bears much resemblance to 

 the pectolite found on the Ayrshire coast, consisting of a vein of 

 diverging and interlacing white fibres. 



Seeing that table spar has been formed by the fusion of lime 

 and silica in a crucible, it is probable that the mineral may have 

 been formed in a similar manner, the granitic heat inducing the 

 combination of a siliceous vein with its calcareous matrix. 

 * Communicated by the Author. 



