332 Reports & Proceedings — Geological Society of London. 



finer material is similar in character, and the inclusions in the 

 grains suggest that it has been originally derived for the greater 

 part from such rocks as gneisses and schists. 



Felspar pebbles are abundant in all the coarse beds. They are 

 dominantly microcline or microcline-microperthite, and when broken 

 are found to be perfectly fresh, the lustre of the cleavage-faces being 

 most remarkable. Blebs of quartz are frequently present in these 

 felspars. In many of the rock-sections, grains of microcline and 

 oligoclase, quite fresh and unaltered, are common. Fragments 

 showing the intergrowth of blue or opalescent quartz and microcline 

 are fairly abundant. 



Chert pebbles are plentiful in the coarse beds at the base of the 

 series ; they are also sporadically distributed throughout the upper 

 beds, and in some of these oolitic structure has been observed. One 

 pebble of silicified oolite shows a microscopic structure strongly 

 resembling a structure found in the Torridon Sandstone. A few 

 fragments containing microscopic organisms have also been obtained. 



Mica is not plentiful in the coarser beds, but increases in amount 

 with decrease in grade of the material. 



From the Middle Grits of Airedale a remarkable assemblage of 

 pebbles has been obtained, including the following types : gneisses, 

 granites, schists, quartz- and felspar-porphyries, quartzites, grits, 

 sandstones, and mudstones. One of these pebbles has been recognized 

 as the black schist associated with the Blair Athol-a-Nain Limestone 

 of Scotland. Another pebble is doubtfully referred to the rhomb- 

 porphyry of the Christiania region. 



The results of the investigations into the heavy mineral contents 

 may be summarized as follows, dividing for this purpose the 

 Millstone Grit Series into three more or less well-defined groups : — 



(a) Lower Division — Base of the Ingleborough Grit to the base of the Leathley 



Sandstone. 



(b) Middle Division — Leathley Sandstone to the base of the Flags below the 



Bough Bock. 



(c) Upper Division — Flags and Bough Bock. 



The minerals are in decreasing order of relative abundance: — 



{a) Coarse beds contain garnet, ilmenite and leucoxene, zircon, tourmaline, 

 rutile, monazite and magnetite. 

 Fine beds contain zircon, rutile, garnet, and tourmaline. 



(b) Coarse beds contain zircon, rutile, garnet, tourmaline, ilmenite and 



leucoxene, magnetite and monazite. 

 Fine beds contain zircon, rutile, tourmaline, and garnet. Some of the 

 separations from the shales of Otley Chevin were almost entirely zircons, 

 only a few grains of other minerals being present. 



(c) Coarse beds contain garnet, ilmenite and leucoxene, zircon, rutile, 



tourmaline, monazite and magnetite. 

 The Flags at the base of the Bough Bock contain zircon, rutile, garnets, 



and tourmaline. 



The monazite has been determined by spectroscopical and chemical tests. 



In view of the similar work which is being done among the 



younger sedimentary rocks, it is important to record that, although 



the author has not yet discovered staurolite in the Millstone Grit, 



he has found it to be common in some of the sandstones near the 



