C12 
BELtMNiTES. LOG-AN, OR ROCKING-STONE 
texture, and more subject to shrink in drying, than even the nucleus 
itself ; and being composed of more earth and less crystal, is also 
more friable and soft. The outer circles of this stone are of a much 
harder substance. When the earthy matter in the nucleus and 
first crust of this pebble exceeds its just proportion, the consequence 
v\ill be, that the stone will become an aetites ; or the nucleus, con- 
tracting itself to a small size, on the evaporation of its fluid matter, 
must separate from its first crust, and that also shrinking must be 
drawn backward towards the other crusts; when the cavity will 
become larger between that and the nucleus, and consequently the 
nucleus will rattle in it when the stone is shaken. The pebble in this 
state having been afterwards rolled away by the waters, the nucleus 
has by rolling broken to pieces all the inner crust, and it is usually 
found in tiie hollow of the stone, buried in a large quantity of 
w hitish pow der. These eagle-stones are not uncommon in our gravel 
pits. The tetites is also known by the names of eutocium, echites, 
lapis aquilae, aquileus, and lapis pregnans. 
Belemnites. 
These are stones which are vulgarly called thunder-bolts, or 
thunder-stone. They are composed of several crusts of stone, encir- 
cling each other, of a conical form, and various sizes ; usually a little 
hollow, and somewhat transparent, formed of several stride radiating 
from the axis to the surface of the stone, and when burnt, or rub- 
bed against one another, or scraped with a knife, yield an odour like 
rasped horn. Their size is various, from a quarter of an inch to 
eight inches; their colour and shape differ. They are supposed to 
be originally either a part of some sea production, or a stone form- 
ed in the cavity of some w'orm shell, which being of a tender and brittle 
nature, has perished, after giving its form to the stone. They are very 
frequently found in many parts of England, and the country people 
have a notion, that they are always to be met with after a storm. 
They are often enclos,ed in, or adhere to, other stones, and are most 
frequent among gravel, or in clay. They abound in Gloucestershire; 
and are found near Deddington in Oxfordshire, where they sometimes 
contain the silver marcasite. 
Logan, or Rocking Stone. 
This is a stone of a prodigious ske, so exactly poised, that it 
w ould rock or shake with the smallest force. Of these stones the 
ancients give us some account. Pliny says, that at Harpasa, a town 
of Asia, there was a rock of such a wonderful nature, that if touched 
with a finger it w'ould shake, but could not be moved from its place 
with the whole force of the body. Ptolemy Hephsestion mentions a 
gygonian stone near the ocean, which was agitated when struck by 
the stalk of an asphodel, but could not be removed by a great exer- 
tion of force. The word gygonius seems to be Celtic ; for diiringog 
signifies motion, — the rocking stone. Many rocking stones are to be 
