6 GEOLOGY OF THE ISLE OF WIGHT. 



gentle anticline, the centre being near Brook Chine, the deep- 

 red and variegated marls of which are perhaps the lowest rocks 

 seen in the Island. 



The lignite bed described above appen.rs to pass out to sea 

 south of", and therefore below, a similar bed which is seen at Brook 

 Point, but the strata are so variable that it is impossible to speak 

 with certainty. The section at the Point shows upwards of 

 100 feet of red, purple, and blue clay with impersistent bands of 

 sandstone, underlain by 13 feet of grey clay, the lower part of 

 which contains numerous flattened masses of black shining 

 lignite. This lignite band rests upon a bed of hard sandstone, to 

 M'liich the Point owes its existence. It is a whitish or pale-grey 

 rock, about 6 feet thick, containing fragments of marl and clay, 

 and with iron-pyrites abundantly disseminated through its upper 

 part. It is irregularly stratified, and its surface is undulating 

 and covered with fucoidal and hollow vertical markings. 



Below and partly imbedded in this rock lie the scattered trunks 

 of coniferous trees, known as the " Pine Raft.'' They were first 

 observed by Webster in 181 1,"^ but were more fully described by 

 Mantell in 1846.t The trunko lie prostrate in all directions, 

 broken up into cylindrical fragments. They are covered by thin 

 bark, now in the state of lignite, the wood having been con- 

 verted into a black or greyish calcareous stone,J with much iron 

 pyrites. Many of the trees still present traces of woody structure, 

 and the annular rings of growth are clearly perceptible ; but 

 they are traversed also by numerous threads of pyrites. The 

 trunks are generally of considerable magnitude, being from one 

 to three feet in diameter; two upwards of twenty feet in length, 

 and of such size as to indicate a height of forty or fifty feet when 

 entire, were noticed by Mantell. 



The "Pine Raft " can be seen at low water only. During spring 

 tides it may be observed to rest on variegated marls, but all 

 attempts to trace it eastwards from Brook Point have failed, pro- 

 bably on account of its being of local development only. The 

 purple marls forming the cliff above it arc ai)parcntly the same 

 beds th;it have made the great slip of Rovighland, and the Pine 

 Raft, if it is continuous, should be found in the cliff near Sedmore 

 Point ; but though many large fragments of trunks are lying on the 

 beach, there is no bed in the cliff exactly corresponding to that of 

 Brook Point. 



A'' suggested by Mantell, the trees were probably drifted from 

 a distance, in the same manner as the trunks, brought down by 

 the Mississippi at the present day, are deposited in large rafts 

 in the delta of that river. It is not to be expected, therefore, that 



* En<!-lcfie1d's Isle of Wight. 1816. 



t Qtiart. Journ. Geol. Soc., vol. ii. p. 91. 1846. 



X Unlike the trunks in the dirt-beds of the Isle of Portland, which are sili- 

 eified. Professor Wn y pointed out the i)roba>)iIity " that the fossil forest imbedded 

 in the Weald Clay at Brook Point is impregnated with phosphoric acid, instead of 

 carbonic acid, as i* generally assumed." Joum. Boy. Agric. Soc. of England, 

 vol. ix. p. 82. 



