GILLIGAN : THE LOWER PERMIAN AT ASHFIELD, ETC. 
291 
In decreasing order of abundance these minerals would appear 
thus : — hematite, limonite, ilmenite, garnet, magnetite, zircon, tourma- 
line, rutile, staurolite. Only a few grains have been noted of the 
following : — fluorspar, xenotime, apatite, epidote and chlorite, while 
only one undoubted grain of monazite has been seen. 
The heavy residue also contains a number of rounded grains with 
aggregate polarisation tints of the high orders. They possibly represent 
some altered mineral, and consist now chiefly of micaceous material, 
but they are never found in association with any other mineral so 
that their origin is obscure. 
It is interesting to note that Mr. K. C. Burton found that the dom- 
inant heavy minerals of the Yellow Sands at the base of the Permian 
of Durham were : — garnet, zircon, rutile and tourmaline, while the 
sands also contained felspar and mica.* 
Garnet. — This is a very abundant mineral, the grains being usually 
rounded or irregular with no crystal outline. In colour they vary 
from a deep red, through pink to colourless. Frequently they contain 
inclusions. The dodecahedral cleavage is well developed upon the 
surface of some of the grains, giving a zigzag appearance. 
Magnetite. — A large number of rounded grains of this mineral are 
present, the crystal form of the octahedra being rarely seen. 
Fluorspar. — A few isotropic grains showing the octahedral cleavage 
characteristic of this mineral occur, and its low refraction compared 
with garnet is very noticeable. 
Zircon. — Excluding the iron ores, the greater part of the heavy 
residue consists of garnet and zircon. A fairly high percentage show 
a sharp crystal outline consisting of prism and simple pyramid. Others 
are rounded at the termination, due possibly to having had originally 
a number of pyramid faces developed. Zonal structure is common, 
especially in the short and stout prismatic forms. Inclusions also are 
numerous, usually arranged parallel to crystal faces. As is usual in 
the case of zircons occurring in detrital deposits the birefringence is 
very high. 
* Note by Dr. Woolacott to his paper on The Geology of N.E. 
Durham and S.E. Northumberland. — Proc. Geol. Assoc. Vol. XXTV. 
pt. 2, p. 93. 
