chap. xii. Santa Cruz. 383 



there were several rounded ridges about twenty feet in 

 height, some of them as broad as high, and some broader, 

 which certainly had been formed whilst the lava was 

 fluid, for in transverse sections each ridge was seen to 

 be concentrically laminated, and to be composed of im- 

 perfect columns radiating from common centres, like 

 the spokes of wheels. 



The basaltic mass where first met with is, as I have 

 said, 130 feet in thickness, and, thirty-five miles higher 

 up the valley, it increases to 322 feet. In the first 

 fourteen and a half miles of this distance, the upper 

 surface of the lava, judging from three measurements 

 taken above the level of the river (of which the appa- 

 rently very uniform inclination has been calculated 

 from its total height at a point 135 miles from the 

 mouth) slopes towards the Atlantic at an angle of only 

 0° 7' 20" : this must be considered only as an approxi- 

 mate measurement, but it cannot be far wrong. Taking 

 the whole thirty-five miles, the upper surface slopes at 

 an angle of 0° 10' 53" ; but this result is of no value in 

 showing the inclination of any one stream, for half-way 

 between the two points of measurement, the surface 

 suddenly rises between 100 and 200 feet, apparently 

 caused by some of the uppermost streams having 

 extended thus far and no farther. From the measure- 

 ments made at these two points, thirty-five miles apart, 

 the mean inclination of the sedimentary beds, over 

 which the lava has flowed, is now (after elevation from 

 under the sea) only 0° 7' 52" : for the sake of compari- 

 son, it may be mentioned that the bottom of the present 

 sea in a line from the mouth of the S. Cruz to the 

 Falkland Islands, from a depth of seventeen fathoms to 

 a depth of eighty-five fathoms, declines at an angle of 

 0° 1' 22" ; between the beach and the depth of seven- 

 teen fathoms, the slope is greater. From a point about 



