1846.] 



DARWIN ON THE FALKLAND ISLANDS. 



271 



it is exactly at right angles to each flexure. The beds have been 

 crushed into numerous successive folds, one of which is represented 

 in the following woodcut. 



A, D, F. Beds of clay-slate, with cleavage-laminae perpendicular to the horizon. 



E and part of C, Similar beds, with the cleavage at right angles to every flexure. 



B and parts of C. Beds of imperfect, non-laminated clay-slate, with intercalated seams of sand- 

 stone represented by the dotted parts. 



F. Nucleus or core of clay-slate formed by the lateral crushing of the strata, about two feet high 

 and one foot broad. 



These nuclei occur in almost all the folds. 



Captain Sulivan states, that in some of the strata the cleavage 

 "in every part, however much twisted, was perpendicular to the ho- 

 rizon ; " in others " it was perpendicular to every curve." I have 

 never myself seen an instance of this structure, and I believe it is a 

 new and interesting case. 



The remaining facts which I have to give refer entirely to the 

 structure of the ranges, composed of quartz rock. In crossing the 

 eastern island in a N.N. W. and S.S.E. direction, in a line intersecting 

 the head of Berkeley Sound, we find north of it several low, parallel, 

 interrupted, east and west ranges, with their strata all dipping a little 

 west of south, at angles varying between 20° and 40°. South of 

 Berkeley Sound the first range we come to is a short one,, rising 

 like all the others through the clay-slate formation : the strata 

 near the summit of the principal hill are most regularly arched, 

 with a curvature of 28° in the line of our imaginary section, and 

 of from 14° to 16° in the line of the ridge: on the summit itself 

 they are horizontal. A regular, flat-topped, oval dome (of which 

 a section is here given) 

 has thus been produced. 

 A valley having been hol- 

 lowed out near the summit, 

 a very curious scene of 

 natural architecture is 

 presented, which excited 

 the utmost astonishment 

 in the old voyager Dom Pernetti. At the northern and southern base 

 of this hill, the strata, instead of being, as near the summit, dome- 

 shaped, dip directly inwards at angles of 40° and 50° : I have little 

 doubt, from what 1 saw in other places, that these strata form parts 

 (as shown by the dotted lines in the section) of outwardly bulging 



VOL. II. — PART I. T 



Dome-shaped hill of quartz, with strata dipping 

 inwards at both the northern and southern base. 



