of the magnetic Needle. 1 95 
“ and I therefore concluded that there was iron ore in the hills, 
“ of which I had remarked other indications, both here and 
“ in the neighbouring parts.” 
On landing at Pier Head I found the stones lying on the 
surface to be porphyry, of a dark bluish colour ; but although 
I understand this species is usually found to possess some 
magnetic power, a piece did not produce any sensible effect 
upon the needle of the theodolite when applied to it. In the 
following observations the theodolite always stood about four 
feet from the ground, that being nearly the length of its legs. 
I first took an extensive set of bearings from the top of the 
hill, amongst which were two stations whence Pier Head had 
been before set. The first, called Extensive Mount, distant 34 
miles, differed from its back bearing 4 0 35' to the right, and 
the second, island a, distant 2C)\ miles, differed 4 0 45' the same 
way. I now moved the theodolite three yards to the westward, 
and the same two objects bore 2 0 10' to the right of their back 
bearing ; on moving it three yards to the south-eastward from 
the first place, they differed 2 0 to the left ; and on moving the 
theodolite four yards to the northward, the same two objects 
bore i° 10' to the right of their back bearings. On the fol- 
lowing morning I determined to try the magnetism more par- 
ticularly. Taking the theodolite and dipping-needle, I landed 
upon the shore of the Head, whence the top of the hill bore 
N 50° W, about one-third of a mile. The variation of the 
theodolite in this place I observed to be 8° 2' E, and the 
commonly happened that no effect was apparent, but yet I could not trust implicitly 
to the angles, (particularly on the main land,) unless observations for the variation 
were taken before the instrument was moved, or I had a back bearing of some station 
where such observations had been made. 
C c 2 
