digression on the zoological characters of the middle system of the chalk formation, we resume our geological survey of the southern coast. Before we climb St. Catherine's Hill, let the observer for a moment take another glance at the view commanded by the terrace in front of the Blackgang hotel, which affords a coup d'œil of the south-western shores. Looking down the ravine immediately at our feet, the aspect of the scene is singularly wild and dreary, from the sombre colours and fantastic masses of the broken walls of the chine, and the gloomy shade thrown athwart the chasm by the projecting cliffs. On the coast, the greensand strata are seen stretching on to Atherfield Point; and beyond may be distinguished Brook Point, which from this elevated spot appears as a low promontory; and farther west are the chalk cliffs, gradually vanishing away towards the Needles.

Ascending St. Catherine's Hill, a magnificent panoramic view bursts upon the sight. From the summit, a height of between eight and nine hundred feet, when the atmosphere is clear, the eye commands at one glance the grand features of the physical geography of the Island, and the range and extent of the principal groups of strata. We are now on the western extremity of the southern range of chalk downs, which, as previously explained (ante, p. 129), is separated by a considerable district of greensand from the central chain of hills.* This system of chalk downs varies in breadth from half a mile to three miles, and extends six miles in a direction E.N.E. and W.S.W. from St. Catherine's Hill to Dunnose, its eastern termination, which is nearly 800 feet high. The intermediate parts of the range maintain an elevation of from 650 to 800 feet, with the exception of a deep valley on the east of St. Catherine's, through which the road to Niton passes; and another at Steephill, called the Shute or Shoot, above * Refer to the diagram, Pl. VII., and the map, Pl. XX.

Ventnor, traversed by the road to Appuldurcombe and Newport. A marl bank on the side of the Shute abounds in fossils.*

The strata of these hills are nearly horizontal, having only a slight inclination to the south-east. From Ventnor to St. Boniface Down, above Bonchurch,† a distance of three-quarters of a mile, the usual smooth verdant character of the chalk is resumed, and the hills rise to the height of 800 feet, sending off to the northward the lofty range of Shanklin Down, and terminating in Dunnose Point. The

* Mr. Saxby informs me that he has obtained from this locality turrilites, ammonites, nautili, belemnites, and many other marl fossils.

High up on the slope of the hill bursts forth a spring called St. Boniface's Well, to which local legends have attached much veneration.

DEVIATION OF the Plumb-line AT SHANKLIN DOWN.-During the progress of the Ordnance survey, a deviation of the plumb-line from its mean direction was observed in the neighbourhood of Shanklin Down, by Col. Colby, the Director of the Trigonometrical Survey; a considerable attraction of the plumb-line to the south of the Dunnose station having been unequivocally determined, and which is supposed to depend on the intensity of the attraction of the hill. In alluding to this remarkable phenomenon, Sir Roderick Murchison (in his address at the meeting of the British Association of Science at Southampton, September, 1846) observed, “that it is a matter of surprise that this comparatively low chalk range in the Isle of Wight should attract, in one parallel at least, with more than half the intensity of the high and crystalline mountain of Schehallien in the Highlands of Scotland. Can this be explained by the peculiar structure and distribution of the ridge of upheaved strata which runs as a back-bone from east to west through the

a In the year 1774, from astronomical observations made on the mountain of Schehallien by Dr. Maskelyne, it was proved that a sensible disturbance was produced in the direction of the plumbline by the attraction of the dense masses of granular quartz and limestone, and mica and hornblend slate, of which that mountain is composed.

L

siliceous nodules in these strata are always found entire; presenting in this respect a striking contrast to the shattered flints in the vertical strata that form the opposite range at Brading Down. (See Pl. XIII.)

COAST OF THE UNDERCLIFF.-The district of the Undercliff, from the western extremity of St. Catherine's Hill to Bonchurch, is about six miles; and the road from the west passes along an irregular terrace composed of fallen masses of chalk, marl, and firestone, which in the lapse of centuries have accumulated in a talus on the southern escarpment of the Downs. Although subsidences are occasionally taking place, and within the last hundred years from eighty to ninety acres of the upper cliff sank down at one time, the greater part of this singularly picturesque and lovely region has undergone no material change since the Conquest. This is evident from the ancient churches of St. Lawrence and St. Boniface, which are referred by antiquaries to the eleventh or twelfth century.* In travelling from Blackgang to Ventnor, the firestone cliffs are the most important geological feature. Here and there on the road-side are seen accumulations of debris, and projecting crags of chert and sandstone, which from their superior hardness have for years resisted the disintegrating effect of the elements. From the intermixture of calcareous and argillaceous earth resulting from the decomposition of the strata, a soil has been produced which supports a luxuriant vegetation. Even the refractory siliceous rocks are more or less clothed with foliage, for the ivy has insinuated itself into every cranny, and hangs in festoons of verdant tapestry over the cherty peaks.

Island? or is it to be referred to the effect of dense masses of plutonic rock ranging beneath the surface along the line of displacement of the deposits ?"

* Sir Henry Englefield; “Isle of Wight.”