188 Scientific Intelligence Hydrogaphy. 
HYDROGRAPHY. 
7. Extraordinary rise of the Rio de la Plata . — This river, as 
is well known, is flooded at certain periods ; and, like the Nile, in- 
undates and fertilizes the country. The Indians then le^ve their 
huts, and betake themselves to their canoes, in which they float 
about, until the watershave retired. In the month of April, in 1 793, 
it happened, that a current of wind of an extraordinary nature 
and violence, heaped up the immense mass of water of this river 
to a distance of ten leagues, so that the whole country was sub- 
mersed ; and the bed of the river remained dry in such a man- 
ner, that it might be walked over with dry feet. The vessels 
which had foundered and sunk, were all exposed again ; and 
there was found, among others, an English vessel, which had 
perished in 1762. Many people descended into this bed, visited 
and spoiled the vessels thus laid dry, and returned with their 
pockets filled with silver and other precious articles, which had 
been buried more than thirty years in the deep. This pheno- 
menon, which may be regarded as one of the greatest convulsions 
of nature, lasted three days ; at the expiration of which the wind 
abated, and the waters returned with fury into their natural 
bed. — Bulletin Universel . 
MINERALOGY. 
8. Resin form Hydrate of Alumina.— This curious mineral 
substance occurs in very thin crusts, in the plastic clay forma- 
tion in the hill of Bernon, a league and a half from Epernay, 
in France. It has a yellowish-red colour, is semitransparent, 
and friable between the fingers. Its constituent parts are as 
follows : — Water, 0.375 ; colouring vegetable matter, 0.085 ; 
Alumina, 0.295; Lime 0.200; Silica, 0.025; Loss, 0.020; 
= 1 . 000 . 
9. Native Seleniuret of Lead and Native Sidphuret of 
Selenium.— u As Professor Stromeyer has favoured me with a 
copy of his and Professor Hausmann’s paper on a native sele- 
niuret of lead, which was lately read before the Boyal Society of 
Gottingen, I beg leave to send you a notice concerning it. The 
mineral was sent by M. Bauersachs of Zellerfeld in the Hartz, 
to Professor Hausmann, with the observation that it contained 
