122 Oo Log JaMBISIEM CIE 
Shale - - - - - - - . - - - 6 feet 
Sandstone - - : : = = : - - 592-8 ((®) 
Limestone - - - - - - - = - - - I foot 
Green sandstone with calcareous band - - - - - 20 feet 
Calecareous zone - - - - ; = ; - - - O 
White sandstone - : - - - - - - - Si iesAlomss 
Shell limestone fossils - - - - = : - - I foot 
Nodular marl - - - - - Sept & - - 15 feet 
Nodular limestone - - - - - - - Binet 
Our ascent ended here but oe, appeared the gypsum beds 
reposing upon red and white marls as in the Nacimiento region 
and elsewhere. Still above and forming separate terraces are 
the chocolate and vermilion beds, and at the top of the section 
the lower Cretaceous. The creeks or arroyos which traverse the 
gypsiferous horizon come laden. with salt which is epostsed | as 
a white coating upon their beds and banks. 
Having satisfied ourselves both as to the age and the charac- 
ter of the deposits which underlie the great plain, we undertook 
a study of the plains themselves. At the southern end of the mal 
pais which forms the northern boundary of our field of work, 
numerous springs gush out from beneath the thin sheet of black 
basalt. These springs differ from those from the salt valley 
itself, in that the water is not warm nor appreciably salty. It is 
apparent that the lava has served to retain the water which, on 
making its way beneath the sheet, has excavated channels in 
which the water may be heard rushing by one crossing the lava. 
One of these streams in particular, at Mal Pais spring, forms a 
considerable creek which supports a varied plant and animal life 
including fish of considerable size and several crustaceans (Gam- 
marus or the like). The water, before it flows many rods, 
becomes distinctly salty and bitter. Ata little distance to the 
south begins an area of depression which is forty miles long and 
receives the drainage from all directions. This whole area is 
covered with saline efflorescence while all the shallows, when dry, 
as they are most of the year, have considerable deposits of salt 
on the surface and the subsoil or under clays are infiltrated with 
alkaline salts the nature of which will be fully discussed in 
another place 
—— GQ. ee ——————————————eeerereorrreaeee_r | 
