96 



KNOWLEDGE 



[Mat 1, 1898. 



samples of coral mud were obtained (average depth 

 740 fathoms). In colour they were various shades of 

 white, and they contain a very large percentage of carbonate 

 of lime (about 87 per cent.). 



In coral sands the fragments of organisms are larger, 

 and the depth is less. Coral muds and sands cover a large 

 area (see Chart I.). Geologists find analogues of these 

 deposits in some of the Jurassic limestones, such as the 

 Bath freestone and the coral rag. The most extensive 

 coral region is that of the Pacific Ocean. 



The following table shows at a glance the relative areas 

 occupied by the different deposits, and the depths at which 

 they 



A word about the volcanic products, so widely dis- 

 tributed, and the chemical changes they are supposed 

 to have undergone. Messrs. Murray and Eenard have 

 much to say on this subject, and they arrived at the 

 conclusion that the manganese nodules they so frequently 

 dredged up on red clay areas are the result of the chemical 

 alteration of volcanic debris. But perhaps it will be wise 

 not to accept this conclusion as final. Pumice stones 

 occur in great numbers near volcanic centres, e.f/., off the 

 Azores. They vary in size from that of a pea to the size 

 of a football. They are most abundant in deep sea clays, 

 from which the shells and skeletons of surface organisms 

 have been removed by solution ; and are more numerous in 

 the Pacific than in the Atlantic. They have a rolled 

 appearance, and have evidently undergone much decom- 

 position. Peroxide of manganese occurs widely as nodules 

 and incrustations on the sea floor. It is a significant fact 

 that the manganese is in greatest abundance where 

 there have been showers of volcanic ash, and hence it 

 seems likely that it may be a secondary product of the 

 decomposition of volcanic minerals. In the manganese 

 contained in lavas and the carbonic acid of ocean waters 

 we seem to have the requisite means for the decomposition 

 of pumice, the solution of the manganese, and its deposition 

 as peroxide. In some places the nodules distinctly show 

 periods of deposition. 



In conclusion, the work of the Challenger expedition has 

 brought to light a fact of great geological interest ; for 

 when the deposits now forming are compared with the 

 stratified rocks in which the geological record is contained, 

 it is found that the latter are very similar to those forming 

 in shallow water and not to the dee)) sea deposits — at least, 

 not to those of the deeper depressions of the sea floor. 

 Even the chalk formation, which in some points so much 

 resembles globigerina ooze, presents some important dif- 

 ferences, and was probably formed in rather shallower 

 water. Again, rocks resembling the red clay are (with 

 one exception) conspicuously absent from the stratified 

 series. That exception is the "red earth " of Bermuda, 

 which must be accounted for by a volcanic upheaval. In 

 view of these facts many geologists have adopted the theory 

 of " the permanence of ocean basins " as the only satis- 

 factory explanation. In other words, they believe that the 

 great earth-movements of the past have been confined to 



the continental areas and the shallow waters by which 

 they are bordered. No doubt there is much to be said for 

 this theory ; but then abysmal deposits like the red clay 

 may yet be discovered in the rocks of new countries. We 

 cannot stop to discuss this interesting question now, but 

 will only point out that it is difficult to see why the 

 abysmal areas should be always sinking and never rising. 



ON CERTAIN LOW-LYING METEORS. 



By Charles Tomlinson, F.R.S., F.C.S., &c. 

 II. — Phosphorescent Meteors. 



DURING the putrefaction of animal matter a gas 

 may be given off which enters into combustion 

 with the oxygen of the air. This gas, as pre- 

 pared by the chemist, is a compound of three 

 parts of hydrogen with one of phospliorus ; but 

 as seen in Nature, it is largely diluted with air, and then 

 appears, if at all, with a glow more or less feeble. Thus, 

 about the year 1860, the town of Thurso, in the north of 

 Scotland, was thrown into a state of alarm by a luminous 

 appearance which was seen during several nights in an 

 adjoining plantation. It was supposed to be a ghost or 

 spectre, and people preferred to go a long way out of their 

 road rather than pass near it. At length a few bold 

 spirits formed a committee of inquiry, and proceeded one 

 night towards the spot, but on a nearer approach imagina- 

 tion had made the spectre appear so terrible that they all 

 turned tail and retreated home — all but one brave hero, 

 who determined to face the awful apparition, and he 

 advanced up to the very tree that exhibited it, when he 

 found that the light proceeded from a large fish which 

 someone had thrown up into the tree, and this, in 

 decomposing, had generated sufficient phosphuretted 

 hydrogen to produce a luminous glow. 



Many years ago the Curator of the Natural History 

 Museum at Geneva had collected a considerable quantity 

 of impure alcohol, which had been used for the preservation 

 of fishes and other specimens. This alcohol was sent to a 

 pharmacist with instructions to purify it and return it. 

 He accordingly mixed it with chloride of calcium and 

 quicklime, and distilled it. Having thus separated the 

 alcohol from its impurities, he proceeded to expose the 

 residue to the open air, in order to recover the chloride of 

 calcium by evaporating the watery liquid ; but when this 

 had attained a syrupy consistence it began to pour off 

 torrents of phosphuretted hydrogen. This lasted many 

 hours and did not cease until the mass had become com- 

 pletely dry. 



The phosphorus in the above case was derived from the 

 fishes and other animals that had been preserved in the 

 alcohol. In the process adopted for purifying the latter a 

 phosphui-et of lime had been formed. This is a compound 

 well known to the chemist, who prepares it by distilling 

 phosphorus over lime heated to redness. Its modern name 

 is calcic phosphide. When a cold lump of it is thrown 

 into water it becomes decomposed, and gives off bubbles 

 of phosphuretted hydrogen. Each bubble as it bursts 

 takes fire on contact with the oxygen of the atmosphere, 

 and produces a white wreath of phosphoric acid, made up 

 of a number of ringlets revolving in vertical planes round 

 the axis of the wreath as it ascends with beautiful effect. 



Such appearances as these do not, however, belong to 

 low-lying phosphorescent meteors. In their most vivid 

 form they present only a glow. In churchyards and other 

 burial places the phosphorus of the animal body during 

 decomposition in the presence of moisture may form 



