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The Hon. Mr. H. Stranoways on the 
ALLUVIA; or POST-DILUVIAN FORMATIONS. 
The formations which I comprehend under the term alluvial, in 
its most confined sense, now claim our attention. As they are 
contemporaneous, their position can give no system of classification ; 
I shall therefore begin with that which resembles the antediluvian 
formations more closely than the rest. 
Tufa or Tuf, a calcareous deposit from the waters of lakes or 
rivers rising in or flowing over a calcareous district, is found in 
several places on the Ingrian side of the Neva. I shall only 
mention Gastilitzi, where it forms arborescent incrustations re- 
sembling corals, to which moss probably gives their peculiar shape 
and appearance : Ropsha, where the waters of the Strelca and 
tributary streams abound in stalactitic depositions ; Poudost, between 
Doudorof and Gatchina, famous for its quarries ; and Anteleva on 
the Ishora, where the Tuf occurs in the form of distinct balls, of 
the size of a large turnip, being concentric crusts of calcareous 
matter adhering to a nucleus usually very small in proportion to 
the entire mass, and which is commonly a pebble fallen from the 
diluvium on the river side. 
A little above the village of Poudost, situated on a stream which 
rises near Kipen and falls into the Ishora at Gatchina, is an open 
valley, about a verst in width through which the river flows. For 
the space of two versts it is accompanied on each side by calcareous 
depositions, which form also its present bed. There are some 
considerable quarries on each bank, which are now worked chiefly 
for lime : but which have formerly furnished much stone for 
building. The colonnade and porticos, if not the whole of the 
Gazan Church at Petersburg, the Palace at Gatchina, the colonnade 
