THE SUBTERRANEAN WORLD.* POPULAR treatises on natural science are often
interesting, without being instructive. The book before us, however, merits, like other works of the same author on kindred subjects, distinct commendation, for it is not only picturesque, but, in the main, accurate. Dr. Hartwig has industriously collected and duly arranged descriptions of most of the phenomena and materials of the earth. As he relies for the effect of his chapters less upon imagination and exaggeration than is common in such books, most of his accounts of the strange things of the globe may be studied with profit as well as read with pleasure.
The agencies by which geological changes have been and are being effected, the succession and forms of living beings, and the lapses of time during which the earth has existed and has been brought to its present condition, are difficult subjects, on which Dr. Hartwig speaks with brevity and moderation. If we find that his descriptions of the state of the primeval and non-historic in- habitants of Europe as revealed to us by memorials from the drift and from caves are not always quite satisfactory, we have, at all events, access to the most complete stores of informatiou on these topics in the able works of Lyell, Lubbock, and Stevens. It is not to be expected that any one author can treat with equal success the very varied subjects which we find included in the Subterranean World, yet we do not doubt that the readers of this book will be quite satisfied with its exciting stories of earthquakes and vol- canoes, and the mysterious recesses of caves, rock temples, under- ground rivers, and mines which are opened to view in the volume before us.
Subterranean activity, as shown to us in earthquakes and vol- canoes, is one of the most startling and unintelligible of the phenomena of the earth. We do not yet possess an adequate view of the various physical and chemical agencies which are concerned in such convulsions of nature. That water has much to do in the development of the forces and the products of volcanic action does not admit of doubt. But we are still in the dark as to the exact nature of what we may call the volcanic mechanism, while there are many strange products to be collected in lava streams, as well as in lagoons, soffioni, and other volcanic vents which bespeak chemical reactions for which we cannot account. Neither the minute experiments of the laboratory nor the local study of the conditions have, as yet, proved adequate to explain the tremen- dous energy of a Vesuvius or a Stromboli. The rest of a volcano is as hard to account for as its activity, while the distribu- tion of active and extinct volcanoes over the earth does not seem to follow any law. Dr. Hartwig gives us accounts not only
of the older and better-known volcanic eruptions, but several of those which have but recently occurred ; such, for instance, as the submarine eruption in the Bay of Santorin, which in the year 1866 formed two islets of stones and scoriae, one being sixty feet and the other two hundred feet in height. The visits to the craters of active volcanoes form perhaps the most interesting portion of our author's chapters on subterranean fires. Humboldt was particu- larly happy in his descriptions of these geological wonders, bat other travellers have also given us excellent views both of active and extinct craters. Mr. Poulett Scrope in 1820 visited Stromboli, and looking down the edge of the crater, saw there precisely the same appearances as those recorded by Spallanzani more than thirty years before. Three hundred feet below the edge of the crater he saw, amidst shapeless masses of black lava, two rude openings, one giving forth every few minutes with a loud roar a • The Subterranean World. By Julius Hartwig. Loudon: Longman& 1571.
column of vapour, the other opening, some twenty feet across, exhibiting still more distinct signs of energy. For in the latter there was liquid lava, glowing with a white heat, and surg- ing up every twenty minutes to the mouth of the orifice. Then it burst with explosive violence like a huge bubble, discharging a column of dense vapour and red-hot cinders to a height of several hundred feet. The volcanic crater of Kilauea, in Hawaii, is seven and a half miles in circuit, and before you arrive at its active region there are two profound precipices, and then in the midst of a dark rocky floor may be discerned two or three blood-red pools of boiling lava, boiling with almost the mobility of water, and yet generally showing no further sign of activity. But when in 1811 an American explorer, Dr. Judd, descended to one of these red-hot pools, with the intention of ladling out a little sample of the boiling lava, his attention was excited by a slight sinking and then by a rise of the surface, and he had barely time to escape before the boiling stream had flowed over the place where he stood ; very shortly afterwards this lava stream was a mile wide, and had travelled to a distance of a mile and a half. But we must not linger amongst the craters, for we wish to give our readers some notion of one of the other subjects treated of by Dr. Hartwig, namely, caverns. Still we may just note in passing the interesting facts given by the author relating to the sudden formation and sudden destruction of vol- canic cones, of the long-hoarded heat of lava streams—by which when they are twenty years old it is possible to light a cigar—of mud volcanoes, and of the asphalte lake of Trinidad.
Passing over the accounts of earthquakes and landslips, we reach a series of ten chapters devoted to caves and caverns, natural and artificial, and to their inhabitants. To the Mammoth Cave of Kentucky, with its grand chambers and 160 miles of tortuous passages, a brief space is given. This cavern is interesting, not only on account of its size, but by reason of its stalactites, not of carbonate of lime, but of the rarer sulphate called alabaster ; and also for the strange blind inhabitants of its dark waters, which, however, are perhaps less numerous than those of the caverns of Carniola. Baumann's cavern in the Hartz, and the celebrated cave of Adelsberg, with a dozen others, are mentioned, but we have failed to find any notice of the very remarkable caverns which give so singular and romantic a charm to the Peak district of Derbyshire. The Peak cavern itself, the remarkable Bluejohn mine which yields both fluorspar and a singular kind of elastic bitu- men, as well as the caverns in the valley of Winyates. deserved some notice at the hands of our author. The interesting locali- ties of England are not too numerous, yet our text-books of geology too often travel far away to give us illustrations of cavern phenonema which might be obtained at home, as in Derbyshire or the Mendips.
The powerful but simple process by which caverns are hollowed and stalactites formed is clearly described by Dr. Hartwig. It is in fact nothing more than the solution of the carbonate of lime, which is the chief constituent of calcareous and dolomitic rocks, by means of water charged with carbonic-acid gas, that is, the fixed air of the older chemists. Then, when this fixed air once again escapes, the carbonate of lime, no longer held in solution, is deposited in stalactites and stalagmites, in pendants and pil- lars, and those varied and fantastic forms in which the lover of caverns finds it easy to discover close resemblances to a hundred animal or vegetable objects. The adornment of a cavern is, however, sometimes due, not to the carbonate, but to alabaster or gypsum, the sulphate of lime, a substance which is softer and far more soluble than the more common compound. But the artificial cavern of Wieliczka in Poland has been formed, though by artificial means, out of a substance still more easily dis- solved by water, namely, rock-salt, and in 1868 was threatened with destruction owing to the inflow of a powerful spring of water, incautiously tapped when boring for certain minerals containing potash which have been found in other salt mines. Fortunately the lower galleries of the mine at Wieliczka have alone been flooded, and farther damage has been prevented. Among the strange sights of this salt mine is an ancient chapel dedicated to St. Anthony, and hewn out of the solid salt, with seats, altar, crucifix, and life-size statues all of salt. The objects looked, says Mr. Bayard Taylor, like grey marble ; but "all were salt as Lot's wife, as 1 discovered by putting my tongue to the nose of John the Baptist."
We cannot do more than indicate the nature of the chief subjects to which the remaining chapters of Dr. Hartwig's volume are devoted. After an account of the rivers of caverns, and the animals and plants of caverns, we find some notices of caves as places of refuge for the persecuted, for robbers and for hermits, and of eaves as places of sepulture and worship. Then we go back to non-historic times, to European caves where bones of men and relics of humaa handiwork have been found mingled with the bones of the hyaena and the cave bear. Now we are taken to the tunnel of Mont Fajta and told how the rock was bored, then we pass down to the mines and learn how the treasures of the earth in gold and silver, iron and coal, and precious stones are discovered, and of the methods and perils of working them. But merely to enumerate the individual subjects described in the chapters on mines and quarries would extend this notice to an unreasonable length. We can but commend to the reader's attention the interesting volume on work and life underground which Dr. Hartwig has prepared..
Previous page
