The Upper Triassic sediments are assumed to have contained concentrated solutions, which caused, or contributed to, their dehydration and contraction. The contraction of a colloidal mass results in the production of tension planes, and unless compensated by settlement, rupture finally ensues. Relief of pressure by rupture may bring the sohtions into the labile state, when innumerable closely-spaced centres of crystallization will be set up. The crystals, fed by vertically diffusing solutions, grow vertically, so long as contraction and feeding continue. When, at length, contraction attains its limit, further growth is resisted, and the stresses set up, transmitted to the central parting, produce bending and other pressure effects in the veins.

Present industrial conditions have tbrccd the engineering trades of the country to adopt methods of mass production, in order to cope with increases in the cost of raw materials and labour. Specialized trades such as the manufacture of scientific instruments are unable to develop quite on these lines, partly because of the limited demands for their goods, and partly because each job is largely an individual one. In the microscope trade much has been done by systematic shop organization, and at the same time an approach is made to mass production by considerably reducing the number of models made, and standardizing the remainder. Naturally the large models for special work have been most affected.

Graphic methods are often of the greatest assistance in bringing out the affinities of closely related minerals and particularly of members of isomorphous series. An illustration of the use of such a method in the case of a series involving three variables, all of them mutually replaceab]e, has already been given by the author in dealing with minerals of the tapiolite-mossite-rutile series. Recently, in studying a mineral of the spinel group, occurring in serpentine country near Namban, in the South-Western Division of Western Australia, it was found convenient to use a graphic method to bring out its relationship to the type minerals spinel, hercynite, and chromite, and to the intermediate minerals previously described under the names of picotite, chrompicotite, magnesiochromite, and magnochromite.

The only book on precious stones in which fibrolite is taken into account appears to be that of .J. Escard, ‘Les pierres précieuses’ (Paris, 1914, p. 190). He mentions the prehistoric stone implements made of dense fibrolite tbund in France, ~nd also states that the mineral is sometimes used as an ornameutal stone. Examples of such material are represented in ttm British :Museum collection of minerals by: a hatchet, measuring 11×½ cm., of pale yellowish-grey, compact fibrolite from N.W. France ; and a polished knife-handle, 9 cm. long, of greyish-white, transluceut, fibrous material with silky lustre. Clear material of good colour and cut in the form of a faceted gem has not hitherto been described.