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Hot springs.

3. That, at a certain depth below the surface of the earth, there is a source of heat which progressively affects the thermometer as we descend.

4. That the interior heat cannot be derived from the sun or from local chemical changes.

5. That it does not directly affect climates or seasons, or successfully influence the temperature of the surface of the earth, the depth of the ocean, or the atmosphere floating above them. 6. That the necessitudes of climates, seasons, and cycles of years are due entirely to solar influences.

7. That the influence, even at a maximum, does not penetrate to a greater depth than the diameter.

doth part of the earth's

8. That although we have positive evidence of the existence of subterranean heat, we can neither measure its degree, nor, at present, determine its exact rates of increase downwards into the interior.

9. That there is not the slightest evidence to show that the earth is gradually cooling from a high temperature, or that, within the last two thousand years, its temperature has undergone any increase or diminution.

In tropical climates the temperature of perennial springs is some degrees below that of the atmosphere; this is more so in North-Western Africa than the other parts, as the temperature of the water does not increase in the same ratio as that of the air. Below 120 feet of water, however, no variation takes place.

The origin of hot springs may be accounted for from the increase of heat as we descend beneath the surface of the earth, and, since for every 15 yards there is an increase of one degree in a temperate climate, at 3300 yards the heat will be sufficient to boil water.

According to the estimation of Fourier, if below 180 miles the interior of the globe was incandescent, it would be sufficient to raise the surface about a 10th of a degree; and if it be 100 times hotter than red-hot iron, it would take 200,000

years to raise the surface only one degree. However, at 40 or 50 miles it would take only 2000 years to raise it one degree. The heat of the celestial spaces has been the subject of calculation by him and Swemberg, who regarded it to be 50° Centigrade below zero or the freezing point.

From the equator to the poles the temperature of the sea varies but little. On approaching land the thermometer in sea water falls from 4 to 6 degrees.

-Gold Coast

Leone.

Western Africa is subject to those subterranean disturbances Earthquakes which are connected with internal heat. In 1855 the colony and Sierra of Sierra Leone was one evening put to confusion by the shock of an earthquake, which took a direction from east to west. In 1861, 1862, and 1863, Accra, on the Gold Coast, was subject to repeated shocks of earthquakes. In August 1862 a series of shocks were felt; the first was so severe that it destroyed the whole of the stone buildings and fortifications at Christiansborg Castle, Dutch Accra, and James Town; it was felt from below the River Volta to 300 miles along the sea coast, and far into the interior. I was present during this and several other convulsive movements. The noise was very astounding, stunned some of the weak nerved and even strong nerved inhabitants, and deprived some of their senses; it was like the noise of a powerful train passing under a tunnel, or the subterranean peals of thunder of the loudest echoes. Cape Coast suffered also in this subterranean agitation, but to a comparatively limited extent.

There are tangible evidences everywhere that the Gold Coast was the scene of repeated earthquakes and volcanic eruptions. in ages long past. Volcanic scoriæ are scattered in the highways and along the sides of the clumps of hills around which Cape Coast is built. I have picked up several of these so-called stones, which corroborated statements put forward by me some years ago in a small pamphlet, entitled "Geological Constitution of Ahanta, Gold Coast," wherein the volcanic origin of those parts was taken into consideration. We shall revert to this subject in another place.

CHAPTER IV.

1. ELEVATION OF THE EARTH ABOVE THE LEVEL OF THE OCEAN.-
2. THE GENERAL INCLINATION OF THE SURFACE AND ITS
LOCAL EXPOSURE.-3. THE POSITION OF ITS MOUNTAINS
RELATIVE TO THE CARDINAL POINTS.

Elevation.

Gambia site.

THE elevation of a country or place above the level of the sea is of very great importance in a sanitary point of view; the generally acknowledged maxim-the higher we ascend the more healthy we become-is nowhere to be regarded as of greater practical utility than in the tropics. In Western Africa we find that the poorer classes of inhabitants, who occupy mud-huts and sleep on mats spread on the bare mud floor, present a greater mortality than even those who occupy the same species of huts, but sleep on sofas one or two feet above the ground. The frame houses, raised about two feet above the ground by stone pillars, allowing a current of air to circulate under the flooring, are the most healthy of the houses of this description in the tropics, and their inhabitants present less annual mortality than those who inhabit mud-huts.

The site of the British colony on the banks of the River Gambia is so low that it is scarcely two feet above the level of the sea; in some places it is below the sea-level; and Bathurst, every year, is subject, at any very high seas, between July and September, to be inundated, as was the case in 1847 and 1851. Lately Col. D'Arcy, the governer, with his superintendent of police, has worked hard to remedy this state of things;

and a barricade has been made to prevent these unpleasant results.

In the immediate neighbourhood of St Mary's, and at Combo, there are extensive plains of offensive and pestilential swamps, which, during the rains and the blowing of the N.W. and S.W. monsoon, add greatly to the unhealthiness of the colony. For the sum of L.7000, says Major Clerk, R.N., this swamp, covering nearly 1000 acres of land, can be most effectually drained; but the exchequer of the colony being in a very impoverished state, there is no hope this recommendation will be carried out. Bacchou, or Cape St Mary's, is situated on a small Bacchou, or rising ground facing the sea; it is the most healthy spot around Mary's. St Mary's, and has been used as an invalid station from Bathurst.

Cape St

Island.

M'Carthy's Island, another station situated about 250 miles McCarthy's in the interior, is about 5 miles in length and 1 in breadth. During the rains it forms an extensive plain of muddy swamp, with a pool of water dividing it almost in two, and emptying itself into the river. It presents no high ground, and when there happens to be a severe rainy season, the island is almost flooded with water. There are large ditches and trenches made at various parts of Georgetown to carry away aqueous accumulations, but the number is too small for the requirements of the place. Towards the end, and in the beginning of the rains, these pools are converted into muddy swamps, exhaling a most deadly vapour.

M'Carthy's Island is exposed to whatever influence of wind it might be subject to, whether mephetic or hygienic, towards the S.W., W., N.W., N., and N.E. At the east and south it is imperfectly sheltered by a low range of hills in the mainland, which is nearly 200 feet high. The general inclination is

from N.E. to N.W.

The barracks of M'Carthy's, hygienically, should have been built on the range of hills on the mainland, which is known as Fa-to-to hill, situated on the east of the island, on the Nyanney ground. Their elevation is sufficient to moderate the heat,

Albreda.

Sierra Leone site.

which is so intense in the hot season among the swamps of the lowland.

The general, as well as local inclination of the colony at Bathurst, including Combo and Bacchou, is towards the swampy banks of the river, and consequently N.E. to N.W. There are no elevated spots around these stations, no mountain or hills, but one flat plain, which is exceedingly swampy during the rains. A few miles from Bathurst, along the river, is the town of Albreda, formerly belonging to the French, but exchanged for Potendie with the British Government. It is built on the declivity of a small range of hills, and forms a more eligible and important station for the principal seat of government than St Mary's or even the Cape. If the summit of the hill be occupied, it will not be very inferior to Cape St Mary's for healthiness, and very far superior to Bathurst or St Mary's; but in a commercial and political point of view it will be superior to any other point on the River Gambia. At present it is the seat of an extensive trade with the natives, but is neither a military nor a colonial station.

An extensive range of bold lofty mountains, running from W.S.W. towards E., and then shaping itself to the south, forms the peninsula of Sierra Leone. They are, I believe, of a volcanic origin, although many have thought that they must have been produced by a huge process of denudation. The highest of Sugar-Loaf. these ranges is Regent Mountain or Sugar-Loaf, about 3000 feet above the level of the sea, and commanding a most extensive view. Uninfluenced by any local peculiarities, it is subject to all the climatorial changes in the weather, and, from its height, receives the breeze in the very same state from whatever position it may proceed. From Sugar-Loaf the mountain runs towards E.S.E. until it becomes partially lost a little way beyond Hastings, or merges into the Waterloo range, the highest peak of which is known as Mount Horton, which terminates abruptly between Kent and York, facing the Atlantic.

Another range in front, and to the south and east of the former, commencing from Signal Hill, where it is almost 400

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