42 Dr. Heddle on the Pseudomorphic Minerals 



to submarine cables, to be highly objectionable. The employment 

 of a return wire, especially of large conducting capacity, would 

 prevent much of the inductive action which now takes place 

 between the inner conductor (the wire) and the outer conductor 

 (the sea). I believe also that a current of moderate quantity 

 and high tension, such as is developed in my own form of the 

 induction coil (Phil. Mag. Dec. 1856), would be far better cal- 

 culated to overcome the difficulties met with in the Atlantic or 

 other submarine cables, than the contrivances which have been 

 hitherto adopted. 



V. A List of the Pseudomorphic Minerals found in Scotland. 

 By Dr. Heddle*. 



s 



HETLAND ISLANDS. In Mainland, on the west side of 

 Hillswickness, nearly opposite the Drongs, — 



Chlorite after garnet, form dnf, Fig. 1. 



fig.l. 

 Although the garnets are here fre- 

 quently an inch in diameter, yet the cry- 

 stals which have been metamorphosed 

 are those of about the size of a pea, 

 and the altered crystals occur only on 

 the exterior of the rock, — the modifying 

 agent, here evidently external, not having 

 penetrated above three inches in depth : 

 taking this into consideration, along with 

 the situation of the crystals, and seeing that the chief change from 

 an almadine garnet to chlorite consists in a diminution of silica, 

 increase of magnesia, and addition of water, we may conclude 

 that the change has been due to the action of the sea. 



Limnite after pyrites, form P e, fig. 2. 



In Unst; on the north side of Balta Sound, in the large 

 chromite quarry, — 



Serpentine after chromite, form o, fig. 3. 



At the smaller quarry at Hagdale, — 



Kammererite after talc, form a o, fig. 4. 



* Communicated by the Author. 



t The lettering is that adopted by Greg and Lcttsora in their Manual 

 of the Mineralogy of Great Britain and Ireland. 



