Notices of Metnoirs — Professor H. A. Miers on Crystals. 265 



In the steep roll of the bank near the brook, in 40 feet, are 

 represented strata of the 



Great Oolite, 



Fuller's Earth, 



Inferior Oolite, 



Upper Lias, 



Middle Lias, 

 the wasted remnant of a thousand feet of rock and clay of the higher 

 north-west Cotteswolds. 



The dip into the hill on the downs of the Taiuton Great Oolite 

 freestone suggests the probability of a high fault line along the 

 downs parallel with the low line of fault described. It may be 

 safely surmised that the curved line of fault mapped by the Survey 

 joins the one at the Waterworks nearer Tainton, and it is probable 

 that the upper line of fault meets the long fault seen to be treading 

 from east to west above Burford and near Waterloo Farm. 



Addendum. — Note on the Mickoscopio Type op the Marlstone 



OF Tainton. 



The stone is of the usual dull green colour, weathering to a reddish 

 brown. It has the granulated appearance of the bottom stone of 

 North Oxfordshire, though it is really not of so oolitic a type. 



In section it is shown as a mass of ferro-crinoid segments, held 

 together by a matrix of clear calcite of which but little is seen. 

 The segments or plates are pentagonal, ovoid, orbicular, or of 

 irregular shape, and are pierced with rounded openings. 



Scattered throughout the mass are olive -coloured patches or 

 granules of ferrous carbonate, with oolitic grains of the same colour, 

 of ovoid or irregular shape, and of small size. When solidified 

 they pass from a pale olive brown to a deeper rich brown colour. 

 The interspaces and passages of foraminifera and other organisms 

 are filled with the same mineral. There is no trace of concentric 

 banding or lamination in the oolitic grains, which appear to be 

 decomposed rather than fully formed. 



It is remarkable that in strata of such great waste the organic 

 structure of the ferro-crinoid, which I have elsewhere shown to be 

 the main constituent of the Middle Lias ironstone, should remain, 

 and that the oolitic stage should be so feebly developed. 



An Enquiry into the Variation op Angles observed in 

 Crystals, especially of Potassium-Alum and Ammonium- 

 Alum.i By Professor H. A. Miers, M.A., D.Sc, F.R.S. 



CORRESPONDING angles measured on different crystals of the 

 same substance usually differ slightly. On cubic crystals the 

 theoretical angles are known. Pfaff professed to have established 



1 Abstract of a paper read before the Royal Society, March 26, 1903. 



