chap. tiii. Uniform Height of Terraces. 211 



would be very hazardous ; not only is the distance from 

 Maldoriado (where I found upraised shells) to the 

 Cordillera great, namely, 760 miles, but at the head 

 of the estuary of the Plata, a NNE. and SSW. range 

 of tertiary volcanic rocks has been observed, 1 which 

 •may well indicate an axis of elevation quite distinct 

 from that of the Andes. Moreover, in the centre of 

 the Pampas in the chain of Cordova, severe earthquakes 

 have been felt ; 2 whereas at Mendoza, at the eastern 

 foot of the Cordillera, only gentle oscillations, trans- 

 mitted from the shores of the Pacific, have ever been 

 experienced. Hence the elevation of the Pampas may 

 be due to several distinct axes of movement ; and we 

 cannot judge, from the upraised shells round the estuary 

 of the Plata, of the breadth of the area uplifted within 

 the recent period. 



Not only has the above specified long range of coast 

 been elevated within the recent period, but I think it 

 may be safely inferred from the similarity in height of 

 the gravel-capped plains at distant points, that there 

 has been a remarkable degree of equability in the 

 elevatory process. I may premise, that when I mea- 

 sured the plains, it was simply to ascertain the heights 

 at which shells occurred ; afterwards, comparing these 

 measurements with some of those made during the 

 Survey, I was struck with their uniformity, and accord- 



1 This volcanic formation will be described in Chapter XI. It is 

 not improbable that the height of the upraised shells at the head 

 of the estuary of the Plata, being greater than at Bahia Blanca or 

 at San Bias, may be owing to the upheaval of these latter places 

 having been connected with the distant line of the Cordillera, whilst 

 that of the provinces of La Plata was in connection with the adjoin- 

 ing tertiary volcanic axis. 



2 See Sir W. Parish's work on ' La Plata,' p. 242. For a notice of 

 an earthquake which drained a lake near Cordova, see also Temple's 

 ' Travels in Peru.' Sir W. Parish informs me, that a town between 

 Salta and Tucuman (north of Cordova) was formerly utterly over- 

 thrown by an earthquake. 



