and Gravels near Newmarket. 163 
way interferes with the working of the nicols, the revolving stage, 
or other parts of the microscope and can be left in position 
permanently. This method of examination is especially useful for 
the detection of glauconite, magnetite, haematite or any metallic 
minerals, and it might perhaps be of service in the search for 
small traces of gold or platinum in sands and gravels and also in 
the examination of soils for agricultural purposes. If a strong 
source of artificial light is not available, sunlight acts as well, or 
even better in the case of minerals of some shades of colour, but 
unfortunately sunlight is not always obtainable when required. 
The special advantage claimed for this arrangement depends 
mainly on the extremely oblique illumination, which reveals 
clearly pittings and inequalities on the surfaces of the grains, thus 
bringing out the characteristic appearance. Among transparent 
minerals it can be usefully employed for the detection of thin 
flakes of mica, which always lie flat in properly mounted slides. 
Since the light strikes them edgeways, owing to their thinness 
they are practically invisible against the dark background, though 
conspicuous when viewed by transmitted light. This complete 
disappearance of a mineral may be taken as a proof of its occur- 
rence in very thin flakes. By this means also the colours of very 
minute grains are made easily visible. This simple apparatus 
was employed to a considerable extent in the examination of the 
Specimens described in the following pages. 
(1) Pit at Newmarket Station. 
Numerous shallow excavations have recently been opened on 
the slope of the hill immediately adjoming the north side of 
Newmarket station, behind the Coronation Hotel, and from these 
numerous mammalian bones have been obtained. Among the 
specimens preserved in the Sedgwick Museum, Cambridge, 
Mr C. E. Gray has identified the following: Hlephas, Hippopota- 
mus, Rhinoceros, Bos, Bison, Ursus and Cervus. The general 
character of the deposit is best described as brown, rather loamy 
sands and gravels with many fairly large flints: pebbles of other 
rocks are extraordinarily rare, only one or two fragments of 
sandstone being observed. 
After washing, the heavy constituents of the sand were 
concentrated by panning and separated directly in bromoform ; 
a large and very ferruginous residue was obtained, necessitating 
prolonged digestion in strong hydrochloric acid. It then appeared 
that a considerable proportion of the grains that sank in bromo- 
form consisted of glauconite of various shades of brown, green 
and bluish green, coated over with a skin of brown iron oxide. 
These were so abundant that a second separation was necessary. 
11—2 
