the Chonos Archipelago, however, neither the minor details of the coast-line, nor the chain of the Cordillera, nor the subordinate transverse mountain-axes, accord with the strike of the foliation and cleavage: the seaward face of the numerous islands composing this Archipelago, and apparently the line of the Cordillera, range N. 11 degrees E., whereas, as we have just seen, the average strike of the foliation is N. 19 degrees W. There is one interesting exception to the uniformity in the strike of the foliation. At the northern point of Tres Montes (latitude 45 degrees 52 minutes) a bold chain of granite, between two and three thousand feet in height, runs from the coast far into the interior, in an E.S.E. line, or more strictly E. 28 degrees S. and W. 28 degrees N. (In the distance, other mountains could be seen apparently ranging N.N.E. and S.S.W. at right angles to this one. I may add, that not far from Vallenar Bay there is a fine range, apparently of granite, which has burst through the mica-slate in a N.E. by E. and S.W. by S. line.) In a bay, at the northern foot of this range, there are a few islets of mica-slate, with the folia in some parts horizontal, but mostly inclined at an average angle of 20 degrees to the north. On the northern steep flank of the range, there are a few patches (some quite isolated, and not larger than half a-crown!) of the mica-schist, foliated with the same northerly dip. On the broad summit, as far as the southern crest, there is much mica-slate, in some places even 400 feet in thickness, with the folia all dipping north, at angles varying from 5 degrees to 20 degrees, but sometimes mounting up to 30 degrees. The southern flank consists of bare granite. The mica-slate is penetrated by small veins of granite, branching from the main body. (The granite within these veins, as well as generally at the junction with the mica-slate, is more quartzose than elsewhere. The granite, I may add, is traversed by dikes running for a very great length in the line of the mountains; they are composed of a somewhat laminated eurite, containing crystals of feldspar, hornblende, and octagons of quartz.) Leaving out of view the prevalent strike of the folia in other parts of this Archipelago, it might have been expected that they would have dipped N. 28 degrees E., that is directly from the ridge, and, considering its abruptness, at a high inclination; but the real dip, as we have just seen, both at the foot and on the northern flank, and over the entire summit, is at a small angle, and directed nearly due north. From these considerations it occurred to me, that perhaps we here had the novel and curious case of already inclined laminae obliquely tilted at a subsequent period by the granitic axis. Mr. Hopkins, so well known from his mathematical investigations, has most kindly calculated the problem: the proposition sent was,—Take a district composed of laminae, dipping at an angle of 40 degrees to W.