R. H. Rastall — Minerals of Lower Greensand. 217 



in the usual small angular chips and fragments, which are common, 

 Avhile larger grains are less frequent. Eutile includes the usual 

 deep red prisms as well as orange and brownish varieties. The 

 most interesting feature, however, is the presence of garnet and blue 

 amphibole in exceedingly small quantity : in fact, the typical sample 

 contained only one grain of each. In their characteristic features, 

 shape, size, and degree of rounding these exactly resembled crystals 

 from the sands of Hunstanton and "West Norfolk. The significance 

 of this fact will be dealt with later. 



4. Great Gransden'. 



This interesting exposure is somewhat difficult to find, as it is 

 situated in a small orchard behind a cottage in the straggling village 

 of Great Gransden, some 3 miles N.E. of Gamlingay. The orchard 

 is really an old quarry, but most of it is now overgrown. On one 

 side, however, the rock is well exposed and appears to show a very 

 sharp dip of some 40°. It is clear, however, that this is in reality 

 current-bedding. 1 



Fig. 2. — Zircons, Great Gransden. x 200. 



The rock here is of a yellowish colour, and rather coarse in 

 texture, some layers being almost conglomeratic, with small and 

 well-rounded pebbles of quartz, chert, and lydian-stone. There is 

 nothing remarkable about these or about the lighter portion of the 

 finer constituents, but the heavy minerals after separation are 

 interesting, and as might perhaps be expected from the generally coarse 

 texture of the rock, they are of fairly large size. In particular, 

 some of the staurolites reach a diameter of 0*5 mm. 



The most abundant mineral is zircon in numerous varieties, to be 

 hereafter described, while rutile is also very common. Staurolite, 

 though in large pieces, is not very abundant, and the same remark 



1 Fearnsides, Natural History of Cambridgeshire (Brit. Assoc. Handbook), 

 Cambridge, 1904, p. 22. 



