128 ORIGIN OF THE ISLE OF WIGHT. 



to west : it consists of the rocks which are called Cretaceous in the 

 southern part, and in the north of those called Lower Tertiary lying 

 upon them ; all these deposits being more or less turned up on end. 

 For the Isle of Wight forms the southern portion of a great trough 

 or synclinal fold of the strata, which is known as the Hampshire 

 Basin. And the middle portion occupied by the newest rocks 

 comes precisely in the line of the sea now known as the Solent 

 and Spithead. Over this depression an excavation has been worn. 

 It is possible that it may have been originated by the River Avon 

 and the Southampton Biver, at a time when the level of the land 

 was somewhat higher; and then the sea, obtaining access to this 

 shallow channel by a subsequent depression, probably widened it 

 year by year at the expense of the adjacent land, until the com- 

 paratively broad water was formed which severs the Isle of Wight 

 from England. On the southern coast at Brook, the Wealden beds are 

 seen which correspond with the Wealden strata of Swanage Bay in 

 Isle of Purbeck ; and there can be no doubt but that the Chalk, and 

 all the strata which lie beneath it at the western end of the Isle of 

 Wight, were continuous with Dorsetshire when the uplifting first took 

 place. It will be observed that, since the strata on the southern 

 shores of the Island all dip to the north, the synclinal fold which 

 forms the island might be prolonged up into the air southward of the 

 Isle of Wight, so as to form an anticlinal fold south of it. Such an 

 anticlinal fold, more or less complicated, inevitably existed when the 

 island first began to be upheaved ; but since rocks, of a brittle 

 nature like chalk, are easily cracked along the direction in which 

 they are bent, it must be concluded that the rocks became fractured 

 along the axis of upheaval, and that the part of the anticlinal fold 

 to the north of this fracture or " fault " was squeezed up out of the 

 ocean, while the other or southern portion was excavated by denuding 

 agents. Not that such fractures could have determined the southern 

 outline of the island entirely, because that is to a large extent 

 obviously attributable to the eroding action of the sea now going 

 on ; but that there are many indications of minor faults in the 

 strata of the Isle of Purbeck ; and it is probably owing to small 

 parallel fractures which run through the island that the Upper 

 Greensand between Ventnor and Blackgang has slipped down 

 bodily towards the sea, so as to form the Undercliff. Thus the Isle 

 of Wight must be considered to owe its existence partly to anti- 

 clinal and synclinal folds of the earth's crust, partly to fractures 

 running through the rocks, and to denudation along these lines. 



Isle of Man. Other conspicuous islands are the Isle of Man and 

 Anglesea. The Isle of Man consists chiefly of Upper Cambrian 

 rocks, with a small mass of Carboniferous limestone in the south. 

 This Upper Cambrian or Lower Silurian is obviously continuous 

 with that of the Lake country of Cumberland and the opposite coast 

 of Balbriggan in Ireland, and the island is an extension of that 

 anticlinal fold towards the south-west, similar to the south-westerly 

 extension of the Silurian rocks of Wigtown and Galloway towards 



