66 



KNOWLEDGE 



[Apkil 1, 189S. 



it is easy to trace the gradual rotting away of these shells 

 with increase of depth. Fragments of volcanic minerals 

 are always associated with the globigerina ooze, and, as this 

 fact was ignored or unperceived, it was not unnatural to re- 

 gard the red clay as something belonging to the ooze itself. 



Messrs. Murray and Renard speak of the red clay as a 

 purely chemical deposit, universally distributed in the 

 ocean basins, but often obliterated by admixture with 

 organic oozes, or with mechanical deposits such as mud 

 and sand. It undoubtedly has undergone much chemical 

 change, and in view of this fact, perhaps it would not be 

 a bad plan to class this curious substance by itself as a 

 chemical deposit. We should then have three groups as 

 follows: (1) ('lu'iiiical dejiasit (the red clay, with its man- 

 ganese nodules and secondary products) ; (2) Pclatjic 

 deposits (all the organic oozes) ; and (3) Terriiienous deposUs 

 (muds, sands, gravels, all mechanically formed). By this 

 arrangement we should avoid the difficulty above pointed 

 out, viz., the question how far it has a truly terrigenous 

 origin, like the various muds. 



The colour vanes greatly in diti'erent samples, but red 

 is the prevailing colour, and hydrated silicate of alumina 

 is always present. Sometimes it is brick red, at other 

 times of a chocolate colour, from the presence in great 

 abimdance of minute grams of manganese peroxide ; and 

 sometimes of a bluish tinge, from the presence of organic 

 matter and sulphide of iron (but only near a continent 

 with large rivers flowing into the sea). The average per- 

 centage of carbonate of lime is 6'7, and the amount of 

 lime gets less as the depth increases. Foraminifera may 

 make up as much as twenty per cent, of it ; of these some 

 live at the bottom, but the majority are pelagic, and come 

 from the ocean surface. Together with thousands of 

 sharks' teeth (preserved on account of their enamel), and 

 ear-bones of cetaceans, are found numerous large and 

 small fragments of pumice and other volcanic materials ; 

 also an abundance, in some places, of manganese nodules. 

 How the latter have been formed we cannot stay to consider 

 now. Remains of pelagic organisms, with siliceous shells 

 or skeletons, are widely distributed in the red clay. When 

 radiolarian remains increase so as to form a considerable 

 part (as in some tropical areas of the Pacific and Indian 

 Oceans), the deposit passes into a radiolarian ooze. When 

 diatom remains (frustules) similarly increase (as in the 

 Southern Ocean) it passes into a diatom ooze; and in 

 other regions, according to the depth, into a globigerina 

 ooze, or even a blue mud. The siliceous spicules of sponges 

 were also found in nearly all the samples. 



According to the ChaUenijer researches, living organisms 

 appear to be universally distributed over the floor of the 

 ocean ; but they are much less abundant on the red clay 

 areas than on any of the other kinds of marine deposits. 

 In the greatest depths, far from land, there is a relative 

 scarcity of life ; but even there it cannot be said that 

 nothing lives, as was thought at one time. Star-fishes, 

 echinoderms, foraminifera, etc., have been dredged up from 

 great depths. Fragments of pumice are very widely dis- 

 tributed throughout the ocean Hoor, varying in size from 

 masses larger than a man's head down to the minutest 

 particles, and they are met with in all states of disintegra- 

 tion — some little altered, others surrounded by zones of 

 chemical alteration ; they are often coated with peroxide 

 of manganese. What the authors call " fine washings " 

 (amorphous clayey matter) make up by far the greater 

 part of the red clay and the greater the depth the greater 

 the proportion of the mysterious clayey material. This is 

 an important fact, evidently pointing to loug-contmued 

 chemical action. The mean percentage of fine washings 

 in the seventy samples reported on was 85-3. The 



mineral particles are mostly very small — the majority of 

 them ranging from 0-1 to 0-85 millimetre in diameter. 

 In some cases wind-borne particles from neighbouring land 

 have been traced and in other cases ice-borne fragments — 

 for example, portions of ancient continental rocks, such as 

 granite, mica-scliist, kc. In the western North Atlantic 

 they were abimdantly found as far south as the latitude 

 of the Azores, and must have been brought down by Arctic 

 icebergs which melted as they reached warmer waters. 

 Lastly, the red clay in some localities is found to contain 

 crystals of the class of minerals known as " zeolites," 

 which are the result of certain chemical changes in the 

 material of the clay. 



Eadiohirian (hi-e. — Silica is not nearly so soluble in sea- 

 water as carbonate of lime, and therefore, when the depth 

 is greater than 2500 fathoms (when the foraminifera are 

 mostly dissolved and the red clay begins to be found) and 

 radiolaria abound on the surface, their siliceous skeletons 

 form a large proportion of the material reaching the bottom. 

 So we get a radiolarian ooze. These oozes are confined 

 to the greater depths of the ocean. They resemble red 

 clay in most respects, but differ from it chiefly in contain- 

 ing a much larger number of radiolarian shells, skeletons, 

 and spicules. When a red clay contains twenty per cent, of 

 these beautiful little organisms, so much admired by 

 microscopists, it is classed as a radiolarian ooze. In one 

 sami^le, from a depth of 4475 fathoms, they formed eighty 

 per cent. Radiolaria seem to be slowly dissolved after the 

 death of the organisms that secrete them from the silica 

 contained in sea-water, for the skeletons and spicules are 

 often seen to be reduced to the merest threads. Siliceous 

 organisms average 54-4 per cent. The average depth at 

 which the deposit occurs is 2894 fathoms. 



Readers who live in Loudon should pay a visit to the 

 splendid Natural History Museum, and inspect the beautiful 

 models in glass of the radiolaria, near the corallines. How 

 they have been made is a puzzle to the writer, so exquisitely 

 tine are their long threads. 



Diatom ('hKi'. — Diatoms are also well known to micro- 

 scopists. These organisms, which belong to the vegetable 

 kingdom, abound in cold seas and estuaries. Their cases, 

 or frustules, show structures of great beauty. The ooze 

 that takes its name from tliem is found at all depths in 

 the Southern Ocean. When dried it is nearly pure white. 

 [A huge lump, obtained from the bed of a lake, may be 

 seen in the Botanical Gallery of the Natural History 

 Museum.] Marine diatom oozes contain about fifty per 

 cent, of diatom frustules, mixed with radiolaria, sponge 

 spicules, together with ten or twenty per cent, of carbonate 

 of lime. A great zone of this ooze, of varying width, sur- 

 rounds the south polar regions, and covers over 10,800,000 

 square miles. The low temperature of this region accounts 

 for the small proportion of foraminifera, etc. it contains, 

 for the lime is only ten to twenty per cent. The presence 

 of a good deal of terrigenous matter in this ooze proves the 

 existence of an unknown ice-covered continent round the 

 South Pole. {To lie continiud.) 



THE DISTRIBUTION OF THE STARS. 



By Miss A. M. Clebke, Authoress of " The System of tlie 



Stars" and "A Popular History of Astrotioiiiy durin;/ the 



NinHeaith Century," d-c., d-c. 



THE fundamental difficulty of stellar astronomy is 

 that of rightly inferring the real from the projected 

 places of the stars. Prolonged study is needed to 

 show that they are not scattered at random over 

 the sky. They shine down upon us as if flung 

 loosely over the surface of a sphere, and indeed owe their 



