2° 9 THE ZONES OF THE WHITE CHALK OF THE ENGLISH COAST. B y D R. A R T HUR W.ROWE,F .G.S . V.-THE ISLE OF W IGH T. THE MAPS AND DESCRIPTI VE AP PENDIX BY C. DAVIES SHERBORN, HO N. F.Z.S., AND ANOTE ON CERT AIN SILICEOUS NODULES BY DR . G. T. PRIOR, M.A. [PLATES VlII. to XXIII. MAPS A-F.] (Read December 711" 1906.) THE WHITE C HALK OF THE ISLE OF WIGHT. FROM COMPTON B AY TO A LUM BAY, AND FROM SANDOWN BAY TO WHITECLIFF B AY, WITH A ZONAL ANALYSIS OF THE C ENTRAL C HALK R IDGE FROM T HE N EEDLES TO CULVER CLIFF. CONTENTS . PAGE Introduct ion 2II Compton B ay '" 216 Zone of Rhynch01ulla cuuieri . 2 17 Zone of Terebratulina gra cilis 2 18 Zone of Holaster planus . 22 0 Freshwater Bay : East Side . 222 Zone of !,ficraster cor-anguinum •.•. 222 U • di. {Marsupites-band 223 Zone 0 f ",arsupttes tutu tnartus Ui. f ' ba d tn acrmus- n 223 Zone of Actinocamax quadratus ' 2 24 Fresh water Bay : West Side 224 Watcombe Bay .. 22 5 Zone of "Heras!er eor-anguinum . 22 5 Zone of IWieraster cor-testudinarium .• 226 Zone of Holaster planus. .•.• 227 The Coast from Fre shwater Bay to Scratchell's Bay 2 27 Scratchell 's Bay ..• 228 Zone of lUicraster cor-anguinum . 128 Zone of Jyfarsupites testudinarius J Marsuptles-band 2 29 ) ljintacrinus-band 229 Zone of A ciinocamax quadratus 230 Zone- of Belemnitelltz mucronata 23 1 Alum Bay. ........ ~32 The Cliff Edge from Freshwater Bay to Scratchell's Bay 233 The Old Road at Freshwater Bay . 234 The Military Road, Freshwater : 234 Culver Cliff . 2 35 On Culver Down .• 236 Pno c.: GEOL. Assoc., VOL. XX, P ART 4, 19 0 8. ] 16 210 DR. ARTHUR W. ROWE ON THE ZONES OF .THE The Culver Section ... 2J7 Zone of RIt)'nclto,ulla cuuieri • 239 Zone of Terebraudina gracilis . 24° Zone of H o/aster planus . .. 241 Zone of Micraster cor-testudinarium 242 Zone of Micraster cor-anguinum . • 243 Z f M, . dinari. I Mar supiles-band 244 one 0 arsupites testu ma riu s I Uinlacrinus-band 244 Zone of Actinocamax quadratus 246 Zone of Bd'mnilella mucronata • 248 General Description of the Cha lk Ridge 249 The Pits of the Chalk Ridge ...... 249 The Western Chalk Ridge: The Needles to Shalcombe 252 West High Down and East High Down 253 North side of Afton Down 254­ Shalcombe Down. ....... 256 The Eastern Chalk Ridge: Culver Cliff to Arreton Down 258 Bembridge Down . 258 South side of Brading, Ashey, Mersley, au d Arreton Downs 259 Brad ing Down 260 Ashey Down. 261 Mersley Down 262 Arret on Down . • . • • 263 N orth side of the Downs of Arreton, Mersley, Ashey, Nunwel1, and Brading 266 Arreton Down 266 Mersley Down 267 Ashey Down . 26 7 Nunwell Down 268 Brading Down 268 The Central Mass. •..•.••.. 269 North side of the Downs of Carisbrooke, Apes, Little, Westover, and Pay. .• 26 9 Carisbrooke Down . 269 Apes Down . 27° Little Down . 271 Westover Down 27 1 Pay Down 272 East side of Garstons and Newham Downs, and Sou th Side of Chillerton, Shorwell, Limerstone, Brigh stone, Mott istone, and Pay Downs Carstens Down Newburn Down Chillerton Down Shorwell Down Limerstone Down Brighstone Down Mottistone Down Westover Down Pay Down The Downs of Bowcombe, Idle combe, and Cheverton Bowcombe Down . Cheverton Down . Idle combe Down . Rowridge, Swaintondown Gate, Little Down, and Newbarn Down Rowridge • . Swaintondown Gate Newbam Down Little Down . WHITE CHALK OF THE E NG LISH COAST. 2 I I The Carisbrooke Area, including Mount Joy and Pan Down 280 Mount Joy 280 Pan Down . 281 Carisbrooke . 282 Summary of Information Concerning Chalk-pits 283 Measurements . 28+ Lithological Summary . 287 Zone of R hynchontlla cuoieri 288 Zone of Terebratuiina I!racilis 288 ( D r. G. T. Prior's Report on the Siliceous Nodules in this zone) . 289 Zone of Hoiaster planus . 290 Zone of Micraster cor-testudinarium 290 Zone of },ficraster cor-anguinum 290 Zone of Marsupites testudinarius 29 1 Zone of Actmocamax quadratus 291 Zone of Belemnitd la mucronata 291 Zoological Summary 291 Zone of Rhynchonella cuuier i • 293 Zone of Terebratulina gracilis 295 Zone of H oiaster plan us 298 Zone of Micraster cor-testudinarium 301 Zone of Micraster cor-anguinum 30+ Zone of Marsupites testudinarius 308 Zone of Actinocama::c quadratus 310 Zone of B elemnitella mucronata 313 Conclusion. ....•. 323 List of the Plates with description of the same 328 Note on the Maps of the Isle of Wight which accompany this P aper, and on the Physiography of the Tertiary Sea-bottom. By C. Davies Sherborn 330 Tabular List of Fossils ...... 336 Index to .. The Zones of the White Chalk of the English Coast," Parts I-V. By. C Davies Sherborn. 340 INT RODUCTION. ONG before the scattered facts and generalisations of a L nascent science had assumed concrete form and crystal­ lised into the rationa l science of modern geology, the Isle of Wight was famous among amateurs of the curious for its strangely disturbed rocks and for the beauty and abundan ce of its fossils. It has ever been the parad ise of the mere collector, and in later days has become a Mecca to which most English geologists, and not a few of their continental brethren, have been impelled to make at least one pilgrimage ; and few there are who once having enjoyed its scenes of beauty and scientific interest can deny them­ selves the satisfaction of a second visit. Nor is the reason for this fascination far to seek, for compressed within this little island, measuring but twenty-two and a-half miles in one direction and 212 DR. ARTHUR W. ROWE ON THE ZONES OF THE thirteen in the other, is much that is best in English Cretaceous and Tertiary geology. The luxuriant undercliff, the mighty cliff of the Culver with its uptilted strata, the noble vault of the Grand Arch, the rugged promontory of the Needles, and the many-tinted sands of Alum Bay, all long since immortalised in pen and pencil by Englefield and Webster, are enough to make the scenic reputa­ tion of a mainland, much more that of a tiny island such as this. The Isle of Wight exhibits two ranges of hills-the Chalk Ridge, extending from the Needles to the Culver, and the Southern Mass, capped by outliers of the lower beds of the Chalk. We may at once say that we have no concern with the latter, and have not examined them to see if there be any remnant of the basal beds of the White Chalk. The one thing which catches the eye in search of " features" is the characteristic angular scarp of the Greensand in the Southern Mass, forming as it does so graphic a contrast to the rounded contours of the Chalk Downs. The Chalk which we shall examine is, therefore, limited to the Chalk Ridge, the cliff sections of Alum Bay, Scratchell's Bay, Watcombe Bay, Freshwater Bay, and Compton Bay on the west, together with those of Whitecliff Bay, Culver Cliff, and Sandown Bay on the east. The point which is material when working in the field is that, as we approach the southern edge of the Chalk Ridge, the horizontal strata give place to those which are gently inclined, and that the farther we pass to the north the greater is the inclination of the beds, till when we reach the highest beds of the White Chalk, at the junction with the Eocene, the strata are almost vertical. And so we find that throughout the Chalk Ridge the angle of inclination is always least on the southern side and greatest on the northern side, thus accounting for the fact that the higher beds of the Chalk, usually so soft and easily worked, are if possible harder and more disturbed than the basal beds, which are normally hard and intractable. As a broad generalisa­ tion these statements will be found to apply universally through­ out the Island, but those who examine the whole of the White Chalk here will find that the stress of upheaval, and consequent compression, has operated unevenly at certain points, thus affording local areas which are relatively soft. The most notable example of this is seen at Alum Bay, at the junction of the Chalk with the Eocene, where the mucronata-chalk is so soft that it can be worked with a knife. The flints, as on the Dorset coast, are often shattered, but they are never so comminuted as in the latter district, where they are often reduced to powder, and drawn out in a long line like a streak of coal dust. And just as the hardness of the Chalk varies within the limits of the same zone, so does the shattering of the flints vary, for there are not a few sections where the flints are quite free from fracture. WHITE CH ALK OF THE ENGLISH COAST . 213 A glance at the map (Plate C.) will show that the Chalk Ridge broadens out in the centre to form what we describe as the Central Mass, and the reason for this marked alteration in the configuration of th e Down is that there the lower beds of the White Chalk are both somewhat bent and inclin ed at lower angles than in the eastern and western limbs, thus causing the strata to spread out fan-wise, instead of being compressed within the narrow limits of the more vertical areas.