CHAP. XII. 



Santa Cruz. 



379 



one included soft ferruginous layer, there were some speci- 

 mens of the Cucullcea alta (found at Port Desire in the 

 lower fossiliferous mass) and of the Mactra rugata, which 

 latter shell has been partially converted into gypsum. 



In ascending the valley of the S. Cruz, the upper 

 strata of the coast-cliffs are prolonged, with nearly the 

 same characters, for fifty miles : at about this point, 

 they begin in the most gradual and scarcely perceptible 

 manner, to be banded with white lines ; and after as- 

 cending ten miles farther, we meet with distinct thin 

 layers of whitish, greenish, and yellowish fine-grained, 

 fusible sediments. At eighty miles from the coast, 1 in 

 a cliff thus composed, there were a few layers of ferru- 

 ginous sandstone, and of an argillaceous sandstone with 



No. 31. 

 Section of the plains of Patagonia, on the banks of the S. Cruz. 

 Surface of plain with erratic boulders; 1,416 ft. above the sea. 



212 ft. thick 



322 ft. thick 



592 ft. thick 





Paver of S. Cruz ; here 280 ft. above sea. 



a. G-ravel and boulders. b. Basaltic lava. 



c. Sedimentary layers. d. Bed of small pebbles. e. Talus. 



concretions of marl like those in the Pampas. At 100 



miles from the coast, that is at a central point between 



1 At this spot, for a space of three-quarters of a mile along the 

 north side of the river, and for a width of half a mile, there has been 



