422 



Mr. Darwin on the Boulders 



Magellan, which are worthy of description. The cliffs are composed of the usual 

 blackish indurated till, in some places interstratified with yellowish argillaceous 

 sandstone, including a few large pebbles. In one cliff about twenty-five feet high 

 (Fig. 2, which is traced from an outline made upon the spot), the main part con- 



Fig. 2. 



Strata dipping 

 N.W. 65° 



B. Yellow sandy mud. 



D. Blackish mud or sandy clay. 



E. A stratum which gradually disappeared in the surrounding mass; its 

 included layers were much convoluted. 



Gregory Bay in the Eastern Part of the Strait of Magellan. 



sists of finely laminated yellow mud (B) , which, a little further to the right, in- 

 cludes many fragments of rock and loses its laminated character. On the left it 

 alternates with layers of blackish mud (D), which are inclined at an angle of 65°, 

 and at the foot of the cliff form a regular saddle. Many of these layers lose them- 

 selves in the yellow sandy mud in the most singular convolutions. In another cliff. 

 Fig. 3. a bed, about eighteen inches thick and thirty feet in length, of fine sandy 

 clay, lying in a coarser sort, dips gently at one end, and at the other is bent back 

 under itself. The subordinate layers in this stratum are curved in basin- , or rather 

 urn-shaped folds about a foot wide, and are placed at nearly equal intervals, so as 

 to resemble some architectural ornament. They cannot always be traced from one 

 basin to the other. The extreme degree of their curvature shows that they were 

 not deposited in so many furrows at the bottom of the sea : it may, perhaps, be 

 conjectured, that during the great and unequal pressure to which the whole mass 

 has been subjected, the finer-grained laminated matter of which these urn-shaped 

 basins consist, yielded more readily, and slided in between the parts exposed to a 

 less force. With respect to the agency by which both sections have been con- 

 torted, from the general undisturbed state of the whole country and of the imme- 



