318 



the plane of stratification of the neighbouring sedimentary rocks), in- 

 dicate a more decidedly simultaneous origin, and appear to have been 

 in the state of disintegrated vegetable matter, mixed more or less 

 with earthy mud, and distributed like the beds of sandstone and 

 clays. That these coals were originally clays into which bitumin- 

 ous matter was injected will not be countenanced by any one ac- 

 quainted with their structural character, contents and relative posi- 

 tion. There is no bitumen in the Boghead parrot, nor any sub- 

 stance analogous to what has been termed ozokerite from Binny 

 Quarry, to which Dr Bennett has referred. The last substance, 

 indeed, melts at a heat considerably below that of boiling water. 



The pulpy condition of the original material of the parrot coals, 

 must have been favourable for molecular changes usually termed 

 metamorphic, which may have so farmodified the forms and structures 

 of the vegetable tissues as to give them a segregated or concretionary 

 character. 



The author concluded by expressing his regret that Dr Traill, after 

 the discussions which have taken place in the Society should have 

 carried his opinion, that the Boghead parrot was a new mineral 

 species, to which he has given the name of Bitumenite, so very far 

 as to have published it towards the beginning of the last part of the 

 Transactions already referred to ; for the material in question is 

 neither chemically, optically, nor mechanically homogeneous, as de- 

 monstrated in the papers of Professors Bennett and Balfour at the 

 close of the same part of the Transactions. 



2. On Errors caused by Imperfect Inversion of the Magnet 

 in Observations of Magnetic Declination. By William 

 Swan, Esq. 



The direction of the Magnetic Meridian, as indicated by that of a 

 freely suspended magnetized needle will generally be erroneous, unless 

 the magnetic axis of the needle is parallel to its axis of figure ; and 

 hence, in order to obtain an accurate value of the magnetic declina- 

 tion, it becomes necessary to take the mean of two observations of the 

 needle, first suspended in its usual position and next inverted. If, 

 however, the inversion of the needle is not accomplished with perfect 

 accuracy, the correction, for want of parallelism between the 

 magnetic axis of the needle, and its axis of figure, will not be com- 

 plete ; and the value of the magnetic declination obtained from the 



