314 OBSERVATIONS ON THE MAGNETIC DIP, 
rate chart calls for a multitude of observations still to be made, yet it is not useless to 
excite the inquiry, 7s the line traced right, or wrong? and, at the same time, to. point 
out where observations are needed, the most readily to determine the chart lines. Could 
the results of the observations made by Major Graham, in the north-east parts of the United 
States, by Professor Bache, in Pennsylvania, New York, and along the St. Lawrence, and 
those in the western portions by Professor Loomis, be united, and my own added, the 
chart would be more extensively determined. 
Plate No. 44.—This is copied from Major Sabine’s Report. It shows the relative 
position of the astronomic pole, the pole of dip and of convergence, discovered by Ross, and 
the pole of maximum intensity, approximately settled by the observations of 1843. These 
are nearly on the same meridian, and not far from twenty degrees asunder; 85° to 90° west 
longitude, and 473°,-70°, and 90°, north latitude. I have also retained Colonel Sabine’s 
lines of 1.6, 1.7, and 1.8, showing that his anticipation of the general configuration of the 
isodynamic curves has been so far sustained by actual survey. We should naturally 
suppose that the pole of dip and of convergence would be also the pole of intensity; but 
research shows it to be otherwise, and it is another amongst numerous instances in 
which Baconian induction has overthrown dreams not founded on experiment. This 
interesting fact, that these points are separate, was also pointed out by Colonel Sabine. 
Plate No. 45.—This plate is intended to show the situation of Porter's Island, the locality 
at which I found the greatest intensity. The general chart No. 1, will show the general 
situation of Copper Harbour, on the extreme northern edge of Kewenon peninsula. The 
lower figure on the plate shows Copper Harbour on a large scale, with Porter’s Island, as 
part of the barrier between the harbour and the lake, just over the words Copper Harsour. 
The upper figure represents Porter’s Island on astill larger scale, showing the topogra- 
phy and geology. ‘The right hand part marked, “dare conglomerate rocks,” is composed 
of imperfectly stratified brown rocks, rising from the lake at an anglo of 30°, and over- 
lapping at the words ‘‘conglomerate ends,” a sandstone changed by heat into a kind of 
trap rock. At this junction of the rocks a sudden magnetic change is evident, the dip 
is suddenly increased by a quantity equal to 1° 3’. The several magnetic stations re- 
ferred to in the text, are here marked by numbers beginning at the extreme west, 1, 2, 3, 
4, &c., to 7, at “Magnet Inlet,” and 8 and 9, beyond or east of it. At Magnet Inlet the dip, 
78° 45’, and the intensity, 1065, are engraved. Here, in passing from station 6 to 7, 
about 500 feet, the dip increases more than one degree. At the east end of the island is a 
section of the rocks of which it is composed, enlarged to twice the scale of the Island 
itself. East of Copper Harbour is a sketch of a copper vein, the spar, including the ore, 
being about ten feet wide. Ata little island east of Porter’s, is marked “Metallic Copper.” 
‘To prevent mistake, it is proper to note that this island is composed of conglomerate rock 
on which some small pieces of metallic copper have been found. The topography of this 
harbour is a type of that of the coast for many miles; the upturned edges of the dipping 
strata throwing the coast into ridges parallel to the shore, and giving an oblong and 
parallel form to the inlets, bays, harbours, lakes, and islands. The portion marked 
“Houghton’s Lake,” is a distinct lake, communicating with the harbour by a river, having 
several feet of fall. By the side of this river was another magnetic station, and upon the 
isthmus to the east, still another. 
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