190 Elevation of La Plata. pake n. 



follow up the same subject along the shores of Chile and 

 Peru . 



On the northern bank of the great estuary of the 

 Eio Plata, near Maldonado, I found at the head of a 

 lake, sometimes brackish but generally containing fresh 

 water, a bed of muddy clay, six feet in thickness, with 

 numerous shells of species still existing in the Plata, 

 namely, the Azara labiata, d'Orbig., fragments of 

 Mytilus edidiformis. d'Orbig., Paludestrina IsabeUei, 

 d'Orbig., and the Solen Caribceus, Lam., which last was 

 embedded vertically in the position in which it had 

 lived. These shells lie at the height of only two feet 

 above the lake, nor would they have been worth mention- 

 ing, except in connection with analogous facts. 



At Monte Video, I noticed near the town, and alone: 

 the base of the mount, beds of a living Mytilus, raised 

 some feet above the surface of the Plata : in a similar 

 bed, at a height from thirteen to sixteen feet, M. Isabella 

 collected eight species, which, according to M. d'Or- 

 bignv, 1 now live at the mouth of the estuary. At 

 Colonia del Sacramiento, further westward, I observed 

 at the height of about fifteen feet above the river, there 

 of quite fresh water, a small bed of the same Mytilus, 

 which lives in brackish water at Monte Video. Near the 

 mouth of the Uruguay, and for at least thirty-five miles 

 northward, there are at intervals large sandy tracts, 

 extending several miles from the banks of the river, 

 but not raised much above its level, abounding with 

 small bivalves, which occur in such numbers that at 

 the Agraciado they are sifted and burnt for lime. 

 Those which I examined near the A. S. Juan were much 

 worn : they consisted of Mactra Isahellei y d'Orbig., 

 mingled with few of Venus sinuosa, Lam., both in- 

 1 'Voyage dans l'Amerique Merid. : Part. Geolog.' p. 21. 



