Professor Jameson oil Trap-Veins. 
its course is parallel with tlie others, and terminates amongst 
them; in another part of its course it intersects these same 
concretions, and then it ends. It is evident, that if this 
concretion had continued parallel with the others through- 
out its whole extent, we would not hesitate to consider it 
as of cotemporaneous formation with them. If this inference 
be admitted, and we do not see on what ground it can be 
refused, it is evident, that, if the intersecting portion of the 
concretion is a continuation of that parallel with the other, 
both must be considered as having crystallized at the same 
time, and as a simultaneous formation with the whole rock in 
w^hich it is contained. But the tabular concretions intersected 
by the one part of the concretion, are equivalent to veins or 
dikes, because they are tabular masses intersected by another 
tabular mass ; and as all these concretions are of simultaneous 
formation, it follows, that the crossing concretion and that 
which is crossed, which are equivalent to two veins, of which 
the one crosses the other, have been formed at the same time. 
Edinbuegh, April 1819. 
Art. XXVIII. — Notice respecting a Singular Optical Pro- 
perty of Tahasheer. By David Brewster, LL.D. F.R.S. 
Lond. and Edin. Communicated by the Author. 
The substance called Tahasheer^' ^ has been long known in 
eastern countries, and formed an important article in the Materia 
.Medica of the Arabian Physicians. In the Gentoo language it 
is called Vedro-Paloo, or Bamboo milk ; in the Malabar, Mun-‘ 
gel Upoo, or Salt of Bamboo ; and in the Warriar, Vedroo Car- 
pooram, or Bamboo Camphor. It is found in the joints of the 
female bamboo, sometimes in a fluid state like milk, sometimes 
with the consistency of honey, but generally in the form of a 
hard concretion. Some specimens of it are transparent, and 
resemble very much small fragments of the artificial pastes made 
in imitation of opal ; others are exactly like chalk ; while a 
third kind is of an intermediate character, and has a slight de- 
gree of translucency. 
* Pliny dearly describes Tabasheer under the name of Sugar. The word is 
derived from the Persian Scher, or the Sanscrit Ksckiramy signifying milk. See 
Humboldt on the I^atuval Family of the Grasses. 
