Nov. 1, 1867.] 



HARDWICKE'S SCIENCE-GOSSIP. 



259 



MICROSCOPY. 



Origin or Rocks revealed by the Micro- 

 scope.— When sedimentary rocks are of subaqueous 

 origin, as is by far the most common case, subaerial 

 or subaqueous outbursts may force into the sea 

 eruptive rocks, which, being- at once broken up into 

 a state of division, more or less fine, in proportion 

 to the greater or lesser cooling power of the water, 

 mass in immediate contact, may be spread out into 

 beds by the action of the waves : the texture of 

 these rocks may vary from that of the coarsest 

 breccia down to the finest mud, and, as is usually 

 the case, such deposits may present themselves as 

 alternating beds of coarse and fine character. 

 Upon the consolidation of such formations, rocks 

 are formed, identical in chemical and mineralogical 

 composition with the original eruptive rock from 

 which they were derived, and which, particularly 

 when close-graiued, often present an external 

 appearance so like the original rocks as to be fre- 

 quently undistinguishable from them by the naked 

 eye ; in such deposits it is often easy to pick out 

 specimens having all gradations in appearance from 

 the above described down to such as would be 

 attributed to the consolidation of mere detrital 

 mud. No wonder, therefore, if the field geologist 

 finds himself bewildered under such circumstances, 

 and inebned to settle down in the comfortable 

 belief of the transmutation or transition of sedi- 

 mentary rocks into eruptive, &c, and even the 

 chemist feels puzzled, when lie finds that a rock 

 taken out of apparently normal stratified deposits 

 has the same chemical composition' with one of 

 undoubtedly intrusive nature. The microscopic 

 examination, however, soon shows that, however 

 similar the external appearance of two such rocks 

 might be, their internal structure is totally different; 

 showing in the'primaiy rock the crystallised struc- 

 ture and arrangement previously described, whilst 

 the secondary rock is resolved into a mere agglo- 

 meration of more or less broken fragments of the 

 same minerals constituting the former. In beds 

 formed from the consolidation of volcanic ashes, 

 the microscopic examination occasionally affords 

 evidence as to whether such ashes had been 

 deposited on land, or had fallen into water. — 

 Dr. Forbes, F.B.S., in " Popular Science Review.' ' 



Noctiluca Miliaris. — I have for some years 

 endeavoured to obtain a supply of Noctiluca 

 miliaris from acquaintances and friends who travel 

 by sea to various parts of the globe, but up to the 

 present time all my efforts to obtain them have 

 been unsuccessful. Will you permit me to recom- 

 mend any of the readers of Science-Gossip who 

 reside near the sea-coast to make a gathering of 

 Noctilucse on any night when they present them- 

 selves in abundance ? Their presence is indicated 



by extensive phosphoresence on the surface of the 

 ocean, each splash of an oar or] ripple of a wave 

 exhibits a phosphorescent luminous appearance — the 

 cause being the presence of myriads of Noctiluca;. 

 If a cambric net be run over the surface of the 

 ocean when the phosphoric light referred to is 

 visible,' it will be found on examination to contain a 

 mass of jelly-like matter, which will consist of in- 

 numerable specimens of Noctilucse. The reason 

 why I desire specially to possess a gathering is, 

 because they" generally contain splendid specimens 

 of diatomaceas in a beautiful condition of purity. I 

 shall esteem it a great favour if any of your 

 sea-side readers would take an opportunity of 

 making a; gathering and send me a portion of the 

 jelly-like mass. It is of course of no importance 

 whether the Noctilucae be living or dead, the 

 object of chief importance is that they be clearly 

 gathered and be placed in a clean bottle.— T. P. 

 Barkas, Newcastle-on-Tyne. 



Elastic Glue. — As there exists some little diffi- 

 culty in manipulating, not to say obtaining, marine 

 glue, allow me to bring under notice a cement used 

 by bootmakers, which answers admirably for aquaria, 

 troughs, and also cells. I send you a stick herewith, 

 the cost of which is only 2d. It is obtainable at 

 any of the leather-grindery warehouses, and will, I 

 think, be found a desideratum to microscopists, and 

 is known as " elastic glue." — John Bockett. 



Campanularia geniculata. — Prom the egg of 

 this Campanularia there springs a ciliated larva, 

 which attaches itself to a solid body, becomes flat- 

 tened, and then resembles a little cake, which has a 

 cavity hollowed in its substance. In the centre of 

 this, granulations make their appearance, and 

 gradually increase in size, elongate, and are con- 

 verted into a straight hollow stem, which is soon 

 covered by a transparent horny sheath. The current 

 which traverses the internal canal of the stem accu- 

 mulates the granules at the extremity of this latter, 

 aud develops a true,bud, which becomes organized, 

 and assumes the form of an inverted bell, closed at 

 its orifice by a horny membrane. The organized 

 material is soon detached from the inner surface of 

 this structure, and converted into a sort of couical 

 button, from which tentacles are pushed out. 

 Finally, in the centre of this mass there appears an 

 orifice, which eventually constitutes a mouth like 

 that of Hydra. The first polyp is then complete, 

 and, bursting through the membrane, it grows out 

 like a flower which has unfolded its floral envelopes. 

 — Qua fref ayes' Metam or piloses. 



Quekett Microscopical Club.— In answer to 

 those who complain that we did not insert any 

 address in our late article, letters may be sent to 

 " The Secretary," at No. 192, Piccadilly, London, 

 W. 



