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SCIENTIFIC NEWS. 



[Dec. 7, IE 



ever the doctor picked up he had a wonderful name for 

 it. At last the doctor came upon a thing he had never 

 seen before — one of those gigantic flints — and then it was 

 his turn to ask a question : " Why, Paddy, what do you 

 call that ? " Paddy saw his opportunity, and was equal 

 to the occasion. "That, sir," said he, after a moment's 

 consideration — " that, sir, is a Paramoudra." The doctor 

 wrote it down in his note-book, and from that day 

 to this they had been paramoudras. Unfortunately, the 

 name sounds very much like a Greek name, and 

 many persons had puzzled themselves about the 

 Greek derivation of this name. He believed, how- 

 ever, it was only fair to mention that Gaelic scholars, 

 people who were acquainted with all the niceties of the 

 Irish language, assert that " paramoudra " is an Irish 

 word signifying "big stone;" whether the Irishman 

 fell back upon his Gaelic or invented a word on the 

 spot I do not know, but ever since it had retained the 

 name of paramoudra. Now, these gigantic paramoudras, 

 or pot-stones, were very curious and enigmatical things. 

 They would see presently that there were many re- 

 mains of sponges in the chalk, and the nearest thing 

 they could compare with these paramoudras were 

 some gigantic sponges which were found in the sea, 

 and which were known as Neptune's cup. It was sug- 

 gested that as the mud which formed the chalk was 

 gradually being accumulated at the bottom of the sea 

 those sponges got on to it, and they gradually formed the 

 paramoudra. The explanation was, perhaps, not a very 

 good one, but at present they were not able to offer any 

 other. The occurrence of these paramoudras was a very 

 singular circumstance indeed. As he had mentioned, 

 they did not occur near London, but only in Norfolk and 

 North Ireland. 



Now to return to more ordinary flints, with which 

 they were likely to make frequent acquaintance, he 

 would point out the fact that flints were often, when 

 broken, found to be hollow. Every one who had 

 looked at flints must have noticed the circumstance 

 that if you broke some flints across you would find they 

 were hollow in the middle ; and every one must have 

 noticed the fact that flints were sometimes partly black 

 and partly white. Very frequently when flints were 

 broken open they found an outside layer of white, and a 

 great mass of the flint was black, and inside again the 

 mass was white. He must remind them that that 

 difference between black and white flint was a difference 

 of very slight importance. They had already seen that 

 if an ordinary black flint was ground to powder the 

 powder was perfectly white, and there were many 

 similar illustrations to the same effect that might be 

 brought before them, such as a lava known as obsidian, 

 and a piece of the same lava blown up into a 

 froth by the gas which escaped from the mass. 

 It was perfectly white and regular. They had seen how the 

 green water of the sea, when lashed into foam, made a per- 

 fectly white foam ; and the colour of that mass was due to 

 the mode of aggregation of the water, and not to any 

 change in the liquid itself. When the mass was blown 

 into bubbles it became white. He must not enter into 

 the physical cause ot that appearance, which was due, as 

 those who had thought anything about physical questions 

 were aware, to the fact that instead of the light being 

 reflected from one surface it was reflected from a great 

 number of surfaces — from every film of glass or liquid 

 which was formed when the mass was blown up into 

 bubbles. When they came to study the microscopical 



characters of flint they would see why black flint in 

 parts passed into white flint ; but for the present it was 

 only necessary to point out to them that black flint and 

 white flint were varieties of the same substance, and 

 if they analysed them they would find both to consist of 

 silica, and nothing but silica. If they took an ordinary 

 white flint and washed from the outside very carefully, 

 all the adhering chalk, which they could do more readily 

 with a little vinegar or other acid to dissolve the chalk 

 outside, the flint would present a very striking appear- 

 ance. If examined with a lens, it would be found to be 

 covered with unmistakable marks of little shells. On the 

 other hand, if they took one of the hollow cavities and 

 examined the white material of the central part, they 

 would find the white powder consisted of a number of 

 curious little shells, many of which were of great beauty. 

 A well-known geologist, Dr. Hinde, once found one of 

 these paramoudra in Norfolk, and from it he obtained a 

 whole museum of specimens. Carefully washing them 

 out and examining them under a microscope, he found thou- 

 sands and tens of thousands of forms, many of which he 

 examined with great care and described, showing what a 

 wonderful diversity of forms existed in the centre of these 

 hollow flints. This white powder in many cases was not 

 a shapeless mass — a mass of particles having no indivi- 

 duality ; but if it be examined carefully with the micro- 

 scope, it would be found that it consisted of little shells. 

 There was only one point he would call attention to about 

 these shells, and that was that though they consisted of 

 silica or flint now, whatever they did once, if they were 

 treated with vinegar or any acid they were not dissolved 

 like ordinary shells would be, but they remained ; they 

 were, in fact, converted into silica. They would see they 

 were once shells consisting of carbonate of lime, but now 

 they consisted of silica. 



He would point out one or two other facts 

 that they must all have noticed about hollow flints. 

 Sometimes hollow flints have their insides lined with 

 beautiful little crystals, and if they had a lens — and 

 he would advise them all to have a lens and use 

 it — they would find that these little sparkling 

 crystals were quartz crystals just like those beautiful 

 quartz crystals to which he called attention in a previous 

 lecture, only very minute. They were like quartz crys- 

 tals, set very closely together with their points directed 

 towards the central hollow of the flint. In other cases 

 when a flint was broken open the hollow was found filled 

 with a substance forming curious rounded nodular 

 masses, and it was a substance to which mineralogists 

 gave the name of chalcedony. He would have to refer to 

 that chalcedony on a future occasion ; but he would call 

 their attention to the fact that sometimes they were found 

 filling the hollow of the flint, sometimes crystals, some- 

 times the substance known as chalcedony. 



He must also mention a fact you may have 

 observed for yourselves, that sometimes flints have 

 not a uniform colour and texture, but exhibit a 

 curious arrangement of dark and light portions ranged 

 in definite bands. Sometimes they might, in examining 

 a flint, see that those banded portions, as they were 

 called, had been formed after the other portions. They 

 might see that there had been a hollow place in the 

 flint, and that there had been a succession of layers of 

 flint laid down, the layers having different tints, and 

 filling up those hollow places. When such flints were 

 worn into pebbles, they often found that the separate 

 layers yielded very unequally to the process of wearing 



