Prof. T. R. Jones and C. D. Sherbom — Jurassic Microzoa. 271 



olivines in the section it contains magnetite along its cleavage cracks 

 and curved fissures. Magnetite is freely disseminated throughout 

 the rock. With a high power crowds of colourless acicular microlites, 

 perhaps apatite, come into view. A little calcite, showing aggregate 

 polarization, is present as a secondary product. No distinct inter- 

 stitial matter can be detected, and indeed the rock appears to be 

 a holocrystalline dolerite. A porphyritic structure is imparted to 

 the rock by large crystals of felspar, the rectangular sections of which 

 may measure as much as 8 mm. x 2 mm. This felspar shows 

 sharply-defined twin lamellation, and in some sections there are two 

 sets of lamellae approximately at right angles to each other, thus 

 suggesting that the plagioclase is twinned on both the pericline and 

 albite types. From its high extinction-angles, reaching 40°, it is 

 probably a basic felspar near to anorthite. 



VII. Dolerite from Wady es Shielc. 



A medium-grained, dark-brown rock, much altered, and weather- 

 ing with a yellow rusty surface. It presents in thin section a dense 

 network of plagioclase in rather thick rectangular sections, with an 

 average size of 1 x 0-25 mm. They inclose dark greenish-brown 

 granular matter, so disposed in some cases as to give a zonal appear- 

 ance to the sections. Augite occurs in crystalline grains and granu- 

 lar aggregates. The space between the felspars is largely occupied 

 by serpentinous matter, and much of the substance which at first 

 sight looks like interstitial matter is probably a product of alteration. 

 Magnetite is abundant, and scales of red oxide of iron are scattered 

 through the rock. Crowds of minute acicular microlites become 

 visible with a high power. 



A re-examination of the diabase, No. 12 in the Appendix, shows 

 that all the quartz is of secondary origin, and hence the rock is 

 simply a diabase with quartz, and not a quartz-diabase. With 

 reference to the felsite, No. 10, it should have been stated that the 

 description applied only to the particular thin section under ex- 

 amination. 



I am greatly indebted to Mr. J. J. H. Teall, M.A., F.G.S., and to 

 Mr. T. Davies, F.G.S., for having examined with me some of the 

 sections described in these notes. 



VI. — On the Microzoa found in some Jurassic Eocks op 



England. 



By Professor T. Rupert Jones, F.B.S., and C. D. Sherborn, Esq. 



TN the Geological Magazine, Dec. II. Vol. IL 1875, p. 308, is 

 a list of some English Jurassic Foraminifera, a large number 

 of species being there noted as occurring in these rocks. We have 

 lately received, by the friendly courtesy of the Rev. H. H. Winwood, 

 F.G.S., and Horace B. Woodward, Esq., F.G.S., thirteen specimens 

 of the Jurassic rocks from the south-west of England. One of these 

 has yielded a most important series of Ostracoda. Whilst preparing 

 a special monograph, we hasten to offer some preliminary notes on 

 these interesting Jurassic Microzoa, at present merely noting the 



