206 CORRESPONDENCE. 



I understand that recently borings have been made, not far 

 from this locahty, in search of a water-supply for the town, but the 

 project was abandoned because the water proved to be too 

 brackish for household use. 



RoBT. C. Douglas. 

 Manaton Rectory, Moretonhampstead, 

 Exeter; Oct. 17th, 1882. 



To the Editor of " The Journal of the Postal Microscopical Society. ^^ 

 Sir,— 



There seems little doubt that this diatom is more generally 

 distributed than is supposed, for in addition to the locality men- 

 tioned by Mr. Douglas, it is noted by Mr. Davis, in " Practical 

 Microscopy," as having been found attached to algae taken from 

 the canal at Birmingham. 



Although probably not sweet, the canal-water ranging from 

 Stoke-on-Trent to Birmingham can hardly be characterised as 

 " brackish," although possibly that in the ditches round Stafford 

 might be, as the neighbourhood is very low and marshy. 



It is quite possible that, so far as the canal is concerned, the 

 Diatom may have been imported ; but, on the other hand, the fact 

 of its being found in ditches round Stafford is against that view, 

 and it is probable that, if carefully sought after, it would be 

 frequently met with. 



It can, however, no longer be correct to describe it, as it is at 

 the present time in existing authorities, as a purely " marine " 

 organism. 



Stone. E. Bostock. 



Felspar and Oligoclase. 

 To the Editor of " The Journal of the Postal Microscopical Society. ^^ 

 Sir,— 



In No. I. of our Journal, the Rev. J. M. Mello, writing with 



regard to the Felspars, gives the formulae wrong, as all the Oxygen 



is left out. I did not write before, as I thought it would have 



been corrected in the following number. They should be : — 



No. -r.— K, O, Al 0„ 6 Si 0„ and part of the Al O, 



replaced by Fe O , and Mn O , and the K O by Na^ O or 



Ca O. 



No. 2.-Na, O, Al 0„ 6 Si 0„ Ca O, K O, or Mg O may 



2 2 3 o it 



replace the Na O. 



