As far as Scilly Isles and the Lizard’s Point, the great tidal wave, which twice in every twenty-four hours flows in from the Atlantic, maintains pretty nearly the same level on the opposite shores; and this continues as far as Exmouth on the Devon coast, and St. Malo on that of Brittany. But when this great wave reaches the “Needles” which form the westerly point of the Isle of Wight, it divides into two very unequal portions. Of these, the southern and larger portion sweeps round the base of the island, passing Freshwater and Chale and Blackgang, and then rounding St. Catherine’s promontory and running up to Dunnose with scarcely-diminished velocity; but the northern and smaller half enters the Solent, and owing, it is supposed, to the resistance of two shores (by friction) to its progress, advances but slowly, and does not arrive at Southampton Water before the other has made Dunnose and is filling Sandown Bay with a back-stream. This causes many differences in the amount of water at almost any given moment on the two sides of the Isle of Wight, north and south; and it gives rise to many curious varieties of tides, real or apparent. In one spot near Shanklin, my attention was frequently drawn to the fact of a partial tide suddenly flowing, for perhaps the space of an hour, during the time of ebb.
But this is not the only “water-company” here at work, nor is the above the only class of phenomena resulting from such agency. Beside the tide-wave there is the Ocean-current, which is quite a distinct thing. This current is due to a branch of the Gulf-stream; and it flows here from west to east, and from south to north. That is to say, after leaving Newfoundland, so much of it as actually reaches Britain would run up St. George’s channel northwards, and up the English channel eastwards. And although the velocity of this current is but trifling, yet, owing to its unceasing action in one direction, its effects are remarkable. Moreover, it is not affected by the waves; whether the sea be sleeping in a calm or tossed with storms, the motion of the current is the same. The only change as yet observed is when its waters come to the surface and have their temperature lowered by a chill wind; for, this gulf-stream is itself a river of warm water, though its bottom and banks are of the same element cold.
Thus, between tide-waves and currents, changes are going on continually both in the volume and the physical constitution of the sea-water. And this, which might at first on a hasty glance look like casual and unimportant variation, when we come to consider it attentively, is found to be an arrangement fraught with wisdom and beneficence; for it insures continual variations of temperature, it attracts the purifying storms, restores the elastic spring of the atmosphere, and provides for weary man a healthy tonic breeze when he rambles along the beach or scales the face of the cliff. Without the motion imparted by the tides, the sea would probably become putrid. Now the tides depend upon the MOON; yet how seldom do we think of her invaluable services, when we gaze upon her pale face! An Italian once told me that he “loved the moon, adored the moon, never tired of looking at the moon.” And the Padishah,[4] I have heard say, prefers “moon-faced” ladies for his soft companions; but I doubt whether either the pensive Italian or the glittering lord of the Bosphorus ever bestowed five minutes’ thought on the mighty phenomenon of the TIDES.
There are other changes in what may be termed the tidal “high-water mark,” due to the lapse of ages, which the sea has chronicled on the face of many a shore and cliff. It is well known that the coast-line, in this and other countries, has experienced many alterations as to its level. In some places, the ocean has apparently encroached upon the land; in many others, it has receded. One striking index of this latter, and which may be implicitly trusted as proving the fact, occurs where the waters have retired from their former level, and have left exposed to view the remains of an ancient beach. Thus, between Brighton and Ovedean, is found what goes by the name of the “Elephant-bed,” because such fossil bones lie among the pebbles in this part of the cliff. The entire stratum undoubtedly was at one time a beach. Similar phenomena have been traced along the coast-lines of Arbroath and Cromarty shires.
Elsewhere, the sea has gained upon the land; undermining the friable sandstone cliffs, and, as it were, melting down the headlands, so as to change the outline of the coast. But in these latter instances, although “terra firma” has given way, it may be doubted whether the water itself has risen. Wherever it has indubitably done so, to the extent e.g. of submerging a village, I should apprehend the presence of volcanic agency.
[4] Sultan, “Father of the Faithful.”
CHAPTER IX.
GEOLOGY LIES AT THE BOTTOM OF EARTHLY THINGS.