384 Tertiary Formations. paet n. 



half-way up the valley, the basaltic mass rises more 

 abruptly towards the foot of the Cordillera, namely, 

 from a height of 1,204 feet, to about 3.000 feet above 

 the sea. 



This great deluge of lava is worthy, in its dimensions, 

 of the great continent to which it belongs. The aggre- 

 gate streams have flowed from the Cordillera to a dis- 

 tance (unparalleled. I believe, in any case yet known) 

 of about 100 geographical miles. Xear their furthest 

 extremity their total thickness is 130 feet, which increase 

 thirty-five miles farther inland, as we have just seen, 

 to 322 feet. The least inclination given by M. E. de 

 Beaumont of the upper surface of a lava stream, namely, 

 0° 30', is that of the great subaerial eruption in 1783 

 from Skaptar Jukul in Iceland ; and M. E. de Beaumont 

 shows 1 that it must have flowed down a mean inclination 

 of less than G 20'. But we now see that under the 

 pressure of the sea successive streams have flowed over 

 a smooth bottom with a mean inclination not more 

 than 0° 7' 52" ; and that the upper surface of the 

 terminal portion (over a space of fourteen and a half 

 miles) has an inclination of not more than 0° 1' 20". 

 If the elevation of Patagonia has been greater nearer 

 the Cordillera than near the Atlantic (as is probable), 

 then these angles are now all too large. I must repeat, 

 that although the foregoing measurements, which were 

 all carefully taken with the barometer, may not be 

 absolutely correct, they cannot be widely erroneous. 



Southward of the S. Cruz, the cliffs of the 840 feet 

 plain extend to Coy Inlet, and. owing to the naked 

 patches of the white sediment, they are said on the 

 charts to be ' like the coast of Kent.' At Coy Inlet 

 the high plain trends inland, leaving flat-topped outliers. 

 At Port Gallegos (lat. 51° 35', and ninety miles south 



1 ' M6moires pour e :rvir,' ice, pp. ITS and 217. 



