TUFA. 113 
where it is said there came unto our Saviour " a woman 
having an alabaster box of precious ointment/' In 
the National Museum at Paris there is a colossal figure 
of an Egyptian deity, which is cut in a kind of alabas- 
ter brought from the mountains between the Nile and 
the Red Sea. 
180. TUFA, or 1NCRUSTING CAREONAT OF 
LIME, is a calcareous substance deposited by such water as 
is impregnated with lime. 
It clothes, with a stony coat, the smaller branches of trees, 
leaves, moss, plants, and other substances; and thus pre- 
serves them from decay, by protecting them from the action of 
the atmosphere. 
Most of the substances termed by the common peo- 
ple petrifactions belong to this kind of lime. They are, 
however, merely covered with, and by no means con- 
verted into stone. 
The dropping well at Knaresborough, in Yorkshire, 
is particularly celebrated for them. An overhanging 
rock, several yards in depth, has been gradually formed 
of the calcareous matter which the water holds in solu- 
tion ; and, from this rock, it incessantly drops into the 
basin below. The persons who have the care of the 
place constantly keep these petrified articles for sale. 
Even old wigs and hair brooms are subjected to the 
powers of the water, to furnish subjects for attraction 
to the visitors. There are other springs of this descrip- 
tion in Oxfordshire and Somersetshire, and particularly 
at Matlock, in Derbyshire. We are informed that at 
Dalton, on the south side of Mendip, the workmen 
not unfrequently discover large pieces of oak enveloped 
in blocks of stone which are four or five tons in weight. 
Blocks of tufa are, in some countries, cut and used for 
building stones ; and this substance, when burned, be- 
comes an excellent lime. Pieces of it are sometimes 
hollowed, and used as filtering stones. 
In the British Museum there is a human skull com- 
pletely incrusted with stone, which was found in the 
river Tiber. 
