TOSCA GRANITE — SOUNDINGS. 



even a foot, in the height of the water, makes a change of 

 cables'lengths, if not of miles, in the position of the limiting line 

 between water and land. In consequence it is very dangerous 

 for ships to approach that shore ; and, although the bottom is 

 in many places soft, often extremely deep mud, there are other 

 spaces in which hard lumps of tosca* are found, almost as 

 injurious to a ship's bottom as actual rock. I am not aware 

 that there is any granite on the south side of the river Plata, 

 near the shore ; and although the name ' Piedras"' would incline 

 one to suppose there are rocks or stones near it, I could only 

 jfind tosca. But towards the northern shore rocks are found, 

 and the dangerous shoal called ' Banco Yngles,' is said to have 

 a granitic foundation. The ridge, of which the English Bank 

 is the north-west extremit}"^, extends eastward, inclining to the 

 south, considerably beyond a line drawn from Cape Santa 

 Maria to Cape San Antonio, and less than ten fathoms water 

 may be found upon it out of sight of land. Northward of the 

 ridge the deptli of water varies from ten to thirty fathoms over 

 a very soft bottom of bluish mud ; and to the southward of it 

 there are from twelve to three fathoms (diminishing as you 

 approach San Antonio) over a softish bottom of brown or 

 yellow muddy sand.f When it is considered that three very 

 large rivers, besides a host of smaller streams, enter the ocean 

 by the estuary whose more remarkable features we are noticing, 

 that two of those rivers are flooded periodically by tropical 

 rains,| and that very heavy gales assist in emptying or filling 

 the shallow wide gulf, in which floods of fresh water contend 

 against the volume of a powerful ocean ; not only will frequent 



* Tosca is a kind of hardened earth, rather than soft stone, about the 

 consistence of slightly baked clay : it is of a dark brown colour, and 

 varies in hardness from that which is almost stony, to the texture of a 

 sound old cheese. 



t Near Cape San Antonio and Point Tuyu there is very soft mud. 



I The Paraguay rises so far northward, that (excepting a portage of 

 three miles) a canoe may go from Monte Video to the mouth of the 

 Amazon. 



