Lithological Survey of Schehallien. 
traces of the observatories (or rather the huts in which Dr. 
Maskelyne had lived), and the two cairns on the top of the 
mountain, the discovery of the whole chain was a matter of 
some difficulty. By means, however, of the bearings, as 
given in Dr. Hutton's paper, and the assistance of one of the 
guides who had been employed about the survey, we suc- 
ceeded in finding out the stations ; and as they were mostly on 
elevated points, we could distinguish them at a distance with 
sufficient exactness. 
Schehallien belongs to one of the central ridges of the 
Grampians, which, stretching here from about SE. to NW. 
divides the vallies of the Tummel and the Tay. Though it 
be a part of this chain, it stands considerably separate from 
the rest on a base of a form somewhat oval, and having its 
figure distinctly defined by two streams that run, the one on 
the south, and the other on the north side of it. The lowest 
point in this base, which is on the NE. is 2467 feet below the 
summit of the mountain, and about 10 $4 above the level of 
the sea. 
At the NW. extremity, Schehallien adheres to the main 
chain by means of a high ridge, depressed at its lowest 
point little more than 1500 feet under the summit. On the 
opposite sides of this neck the streams rise, which were before 
said to determine the base of the mountain; these streams, 
however, do not unite at the eastern extremity of the base, 
for there also a sort of neck, though very low in comparison 
of the former, connects Schehallien with the hills to the 
eastward. 
Beyond the streams just mentioned, a range of inferior 
hills, some of them very low, springing from the main ridge 
