398 DK. W. HIND AND ME. J. A. HOWE ON THE [Aug. 190!^ 



surface with a lens reveals great Dumbers of minute rounded bodies 

 (possibly foraminifera) with sponge-spicules, hydrozoa, and shell- 

 particles ; crinoidal debris seem less abundant than in the limestone. 

 The matrix is a milky cryptocrystalline silica, transparent in section 

 and colourless, but with occasional amber-coloured patches ; in the 

 less coarse forms there is less of the milky material and more of 

 the amber-coloured silica. Most of the organisms are converted 

 into the amber- coloured silica, but the internal casts are usually 

 filled with a darker, more coffee-coloured material ; in this way 

 the structure of the foraminifera is occasionally very beautifully 

 exhibited. Both the brown and the clear portions of the slide 

 have the same appearance of cryptocrystalline silica when viewed in 

 polarized light. In some of these cherts, the rounded bodies (men- 

 tioned above as visible on the weathered surface) are so crowded 

 together that there is little room for matrix. Their most common 

 form is roughly oval, with diameters of 0*32 and 0*24 mm., but 

 some measure as much as 0'6 X 0'32 mm. Most of these bodies are 

 foraminifera, the genus Stacheia heing very strongly represented. 

 On the whole, they show no internal structure nor wall, but stages^ 

 can be seen in our slides showing every intermediate condition 

 between foraminifera of the same size and general form, with 

 perfect structure, through very indistinctly-marked specimens, to the 

 rounded bodies devoid of all structural detail, frequently a coarse 

 hazy meshwork can be seen occupying the interior of the body, 

 having a dark, dusty appearance in direct transmitted light, but 

 appearing light-coloured by oblique illumination. 



Fragments of irregular meshwork, sometimes clearly of sponge- 

 origin, but more often doubtfully referred to those organisms, are to 

 be seen here and there, composed of iron-oxide. In some of the 

 slides, the dark-brown portions, whether in the casts of organisms 

 or as irregular masses in the matrix, are marked by numerous small 

 circles, generally isolated, but sometimes confluent. In" size they 

 are fairly uniform, ranging from 0*01 to 0018 mm. in diameter. 

 Their outline, except where they merge into adjoining circles, is 

 very sharp, but no wall has been observed. They make their appear- 

 ance in the casts of any of the organisms without discrimination. 



These may be comparable with the bodies described by M. L. Cayeux 

 as radiolaria and foraminifera,^ but considered by Dr. G. J. 

 Hinde,^ who noticed something similar in the more cherty beds of the 

 Devonshire Culm, to show no evidence of organic origin, and with 

 this remark our own observations are in direct accord. 



The rhombs of dolomite, noticed in the limestones, are also present 

 in these cherts ; they do not, however, retain their freshness, having 

 apparently undergone some kind of alteration, and they are frequently 

 surrounded and penetrated by dark iron-oxides. Minute rhombs 

 in a fresher condition occur in the interior of some of the casts as 

 well as in the groundmass. In some portions of the slides are 



1 Bull. Soc. geol. France, eer. 3, vol. xxii (1894) p. 197, & Comptes-rendus 

 Acad. Sci. Paris, vol. cxviii (1894) p. 1433. 



2 Quart. Journ. Geol. Soc. vol. li (1895) pp. 631-32. 



