59Q 



SCIENTIFIC NEWS. 



[Dec. 7, li 



sented only a few of the infinite variety of those exquisite 

 forms of vegetable life. In addition to the plants there 

 were skeletons of minute animals. Those larger organisms 

 were skeletons of animals known as radiolarians. 

 There was a wonderful diversity of beautiful forms repre- 

 sented in a diagram exhibited, but thej' were only a very 

 small selection indeed out of the thousands of wonderful 

 forms that were known and had been described by 

 micros copists. Last of all they would find a number of 

 rods and plates, often assuming very curious forms, and 

 these they would recognise as being portions of the 

 skeleton of curious sponges — of which specimens were 

 on the table — sponges which had skeletons composed 

 entirely of colloidal silica built up into rods and plates in 

 the most complex patterns, as represented in diagrams 

 produced. Now, they found none or scarcely any such 

 objects as those in chalk when it was dissolved in acid, 

 but in the globigerina ooze they would find them. 



He must call their attention for a moment to the 

 chemical composition of the different rocks forming the 

 chalk series. He had already pointed out to them 

 the way in which chemical analysis was carried on, and 

 he had with him some results which had been obtained 

 by analysing some different kinds of chalk, and beds 

 which lay below the chalk in the South of England and 

 elsewhere. Many of those present might have noticed 

 the fact that flints were confined to one portion of the 

 chalk. In the upper part a great thickness of chalk with 

 flints was found, whereas in a lower part there was no 

 chalk flint, and that difference was accompanied by other 

 differences. Chalk which contained flint was of a beau- 

 tiful white colour, and chalk which did not contain flint 

 was more or less of a grey tint. Many of them could 

 recognise in their visits to the seaside that the upper 

 part of a cliff contained flints and the lower part none. 

 If they examined the chalk they would find that the 

 chalk with the flints consisted entirely of the pure 

 substance calcic carbonate, and there was only a very little 

 silica, but if they took a mass of the lower chalk they 

 would find the quantity of carbonate of lime was some- 

 what less, but the quantity of silica was much greater. 

 The suggestion offered itself at once that in the upper 

 chalk the silica had been separated out to make the flints, 

 while in the lower chalk the silica remained distributed 

 through the chalk. Now that was the first suggestion 

 which struck one, and they would presently inquire 

 whether they were able to verify that working hypothesis. 

 If they examined the other beds below the chalk they 

 would find that many of them contained a considerable 

 quantity of silica, and they also contained sand and other 

 substances that could be washed out of them, but into 

 that subject he must not at present enter further. 



Now let them ask two questions that would be of great 

 use to them in their future inquiries : Were there any 

 rocks besides flint which consisted cf silica and silica only ? 

 All substances known as sand and sandstone, and the 

 very hardened variety known as quartzite consisted 

 almost entirely of silica, but they differed from flint in 

 the fact that while flints appeared to have a very uniform 

 texture, when examined by a lens or microscope, the 

 sand or sandstone, or quartzite, would be seen to be made 

 up of little fragments, these little fragments being derived 

 from granite and other rocks which contained the sub- 

 stance silica, so they might put aside sandstone and 

 quartzite as having but little analogy with flint except that 

 they consisted of silica, but their silica had evidently 

 been derived from the breaking up of other rocks. But 



there were other substances which presented much closer 

 analogies with flint. First of all he must call their 

 attention to the fact that in some parts of the world 

 they found hot springs which rose from the ground : 

 the great hot springs which occurred in Iceland, known 

 as geysers, and also in Yellowstone Park, North 

 America, and in New Zealand — these springs coming 

 from the ground boiling hot and rising into the air to a 

 great height, and making great eruptions. But this hot 

 water contained in solution large quantities of silica, 

 and when the hot water cooled down the silica was 

 deposited. The silica left sometimes formed basin- 

 shaped hollows, sometimes masses like cones known as 

 geyser cones, and at other times it formed curious sorts 

 of cups forming most wonderful natural bathing places 

 like the White and Pink terraces which were un- 

 fortunately destroyed in the great eruption of 

 Tarawera in 1886. Now, the silica had evidently 

 been held in solution by the water, and as the water 

 had cooled, that substance had been left behind, building 

 up beautiful and wonderful structures. Just as they 

 dissolved silica in alkali, and then made it separate from 

 the liquid by adding acid, so they had in those cases 

 the like action of the hot waters containing various 

 acids. These acting upon the lavas of the districts, 

 they got silicate of soda and of potash in solution, 

 the silica being left behind in a colloidal form. Now 

 he must call their attention to another class of sub- 

 stance which presented some analogy to flint. They not 

 unfrequently found deposited a mass of materials en- 

 tirely composed of the skeletons of different organisms 

 which had skeletons made up of the substance silica. 

 Many years ago Sir Joseph Hooker found out that at the 

 bottom of the Antarctic Ocean there was a mass of white 

 mud entirely made up, or almost entirely made up, of 

 the remains of beautiful plants — the skeleton of the 

 wonderful diatomaceae, hundreds .of varieties being 

 present in countless millions ; and the observations of 

 Hooker had been confirmed by the explorations of the 

 Challenger and other vessels. In other parts of the 

 ocean, however, they found a great mass of rock, entirely 

 made up of the remains of the diatoms. There were 

 skeletons composed of colloidal silica which were much 

 larger than those of the diatoms, and sometimes they 

 found masses entirely made up of the remains of 

 sponges and radiolarians. In various parts of the 

 country where lakes had been drained or filled up 

 they also found masses of white material which were 

 also found when examined under the microscope to be 

 made up of these minute plants, skeletons of diato- 

 macea?. This substance, which was used for making dyna- 

 mite on account of its great absorbing power, was com- 

 posed entirely of these excessively minute skeletons of 

 this curious plant, the diatoms. In other places they 

 found great masses of rock, as in North America, espe- 

 cially in the Island of Barbadoes, made up of radiolarians, 

 and in other places they found deposits crowded with 

 fragments of the curious siliceous sponges. He thought 

 they were now in a position to profit by the investigation 

 that they would be able to make by aid of the micro- 

 scope, as to the actual structure of flints, and from the 

 study of the microscopic structure of flints he hoped they 

 would be able to draw some inferences as to the probable 

 mode of origin of the flints. It had been necessary to 

 bring those general facts before them in order that they 

 might reason upon the facts that they would observe by 

 the aid of the microscope. 



