88 Meviews — Jukes-Browne 8f Sill — Gauli and IT. Greensand. 



asper has not been found in them or in the topmost bed of calcareous 

 sandstone. 



In Oxfordshire and Buckinghamshire the Lower and Upper 

 Gault clays have been proved by borings in various places to reach 

 a thickness of 14^230 feet. Fossils occur in the Lower Gault 

 which elsewhere in the South-East of England are only found in 

 Upper Gault ; for example, Am. rostratus, Am. varicosus, and 

 Am. cristatus ai*e associated with Am. lautus, Am. splendens, and 

 Am. tuberculatus. The Upper Gault becomes marly, and passes into 

 a micaceous marl and malmstone. 



At Stoke Ferry in West Norfolk the Lower and Upper Gault 

 is represented by a blue clay about 56 feet in thickness ; more than 

 half of it probably belongs to the zone of Am. rostratus. North- 

 wards the clay is replaced by calcareous material and gradually 

 thins out, so that at Hunstanton there is only about 3^ feet of 

 red earthy limestone between the sands of the Lower Cretaceous 

 and the Lower Chalk. The author and Mr. Hill maintain the view 

 put forward by them in 1886 that the Eed Chalk is the actual 

 stratigraphical equivalent of the Gault. They also agree with 

 Dr. Barrois that the zone of Peden asper is wanting in Norfolk, 

 and that there is a direct passage from the Bed Chalk to the 

 Chalk Marl. 



The Red Chalk is shown again in Lincolnshire and in Yorkshire, 

 where it gradually passes into a stiff red marl with calcareous 

 nodules. Mr. F. Chapman has recorded 86 species of Foraminifera 

 from this rock in Norfolk and Yoi-kshire, and 52 of these, or about 

 60 per cent , have been found in the Gault of Folkestone, whilst only 

 25 occur in bed 2 of the Chalk Marl of Eastwear Bay, thus indicating 

 that the Red Chalk has a closer relation to the Upper Gault than 

 to the Chalk Marl. 



In Chapters xxiv and xxv Mr. W. Hill describes the microscopical 

 structure and the mineral ingredients of the Gault, Red Chalk, 

 Greensands, Malmstones, etc. The Gault marls and clays consist 

 in part of very finely divided, apparently structureless material, 

 without reaction in polarized light between crossed nicols ; in part 

 of fine detritus of quartz, mica, and glauconite, with entire and 

 fragmentary tests of organisms. Thin microscopic sections of the 

 Gault do not give good results, and its characters were best 

 ascertained by washing and sifting different samples. 



The coarser particles of quartz, mica, and felspar fragments form 

 but a small proportion in typical Gault clays. Zircon, rutile, 

 tourmaline, magnetite, ilmenite, garnet, and cyanite were also 

 recognized by Mr. Teall. The glauconite occurs in irregular 

 rounded and mammillated grains, seldom more than 0*5 mm. in 

 diameter, also as minute cylindrical rods, apparently moulded in 

 the canals of sponge spicules. Marcasite (disulphide of iron) is 

 also present in the form of small spherules, cylinders, and irregular 

 masses. 



Mr. Chapman has determined 265 species and varieties of 

 Foraminifera from the Gault at Folkestone, and 66 species of 



