1862.] 



DARWIN BUENOS AYRES. 



69 



downwards from the level of the Rio Plata to a depth of 61 feet, 

 and to this must be added 55 feet above the level of the river. 

 These argillaceous beds overlie coarse sand, containing the Azara 

 labiata (a shell characteristic of the Pampean formation), and at- 

 taining a thickness of about 93 feet*. So that the entire thickness 



Fig. 1- 



■Comparative Sections of the Artesian Wells of Bar rams 

 and Buenos Ay res. (Distance 3f miles.) 



Buenos Ayres. 



Barraeas. Riachuelo. 



Level of equi- 

 librium of 

 the princi- 

 pal spring 



1st spring 



2nd spring . 



3rd spring . 

 •4th spring . 



= M 



■J! 



:. 



?-S 



h 



= High-water level. 



^ 



1 



n 



H = 2nd spring. 

 jj = 3rd spring. 



1= 4th spring. 245 feet. 



1*2 



470 feet. 



13 



47 



Thickness at 



Barraeas. 



Feet. 



a. Clays and Tosca 



b. Sand 



c. Very sandy clay ~| 



d. Dark -blue plastic clay > 



e. Tosca with calcareous nodules I 



/. Yellow sands, very fine and fluid 94 



g. Green sands 66 



h. Tertiary clay and sandstone (for details see fig. 2) 34 

 Tc v Hard sandstone at the bottom of the Barraeas 



Well 



£ 2 . Very calcareous red clay, becoming more marly 

 beneath ; bored through to a depth of 



Thickness at 

 Buenos Ayres. 



Feet. 

 57 



51 



^ 



52 



45 

 62 

 33 



225 



* The following extract from the Report of the borers relates to this bed : — 

 " The bed of yellow, fluid sands between 18 m, 60 and 47 m '20 below the ground 



