« ПредыдущаяПродолжить »
your forceps, will cause the thin section to slide off the glass. Drop it into a watch glass filled with benzine, and when it has soaked a little time, wash it thoroughly with a camel hair brush, and get rid of all the balsain that may adhere to it. Break it across where you scored it with the knife. Each piece is now smooth on one side, and more or less polished on the other; the polished side being finished must be attached to a little disc of thin glass termed a cover glass. These can be had of all sizes, and it is well to have an assortment, so as to be able to suit your specimens. A very convenient size is about gin. diam. and that will suit the present purpose.
(6) Your cover glasses being quite clean, warm both them and your specimens, and place on each cover glass a piece of balsam, and when melted lay a specimen, the polished side downwarıls upon it, pressing it firmly and moving it a little to expel any bubbles. A small brass or copper stand with a spirit lamp below it will be found most convenient for warming the glasses and specimen in this and subsequentoperations; one can be obtained, made specially for this purpose at the microscope dealers, or can be quite easily made by oneself. If the rock be at all friable it is well to let it have enough balsam to thoroughly embed it. Be careful that there are no bubbles or air spaces
between it and the glass, and hold it firmly in a pair of forceps for a few seconds, till it is cool. Then take a narrow slip of glass, 3 in. + 1 in., such as are generally used for microscope slides, and attach your cover glass close to one end of it, with a bit of balsam. Press it down with a spring clip, and leave it for a few hours for the balsam to harden thoroughly, and treat the other pieces in the same way.
The glass slip serves for a handle, holding this grind the specimen on a water of Ayr stone till it begins to be somewhat transparent, and then finish it either on a very fine hone, or on a piece of plate glass with Rottenstone. This is perhaps the best, as it is important to grind it evenly, and the plate glass ensures an even grinding surface. The grinding must be done very carefully, and every minute or
so it should be dipped in water, just washed with a brush, and examined with a lens, or else before you know where you are, it will be quite ground away, or have so broken up as to be useless.
as one piece has been made tolerably transparent, put it aside and proceed with the next and as you are now sure of one, you may try to make this next one thinner than the first ; if you succeed in doing 80, you can return to the first, and grind it to the same or a greater transparency. You next warm the glass slips, and very carefully slide off the cover glasses, with the objects attached to them, and wash them in benzine with a camel hair brush.
(7.) The preparation of the object is now complete, and you proceed to mount it on a glass slip, so that it may more readily handled and examined, without fear of injury. The best medium for this is Canada balsam dissolved in benzine, so as to be rather thinner than syrup. You take a 3 + 1 in. glass slip, and, having warmed it on the brass stand, drop a drop of the thin balsam in the centre, and then place the cover glass, with the object downwards, of course, upon it, letting one edge down first, and then closing it down like the lid of a box. Press it firmly down, and keep it so, either with a spring clip or lead weight; and leave it a short time, on the warm stand, but be very careful not to let it get hot enough to form bubbles (the thinner the balsam the less liability to bubbles). Then remove any superfluous balsam, and put the slide aside for some days, where it will be free from dust. When it seems quite firmly set, wash off any balsam that may be sticking to the glass with a camel hair brush and benzine, and wash off the benzine with another camel hair brush and some soap and water. When dry it is quite ready for the cabinet, but it will be better able to resist any comparatively rough usage or accident, if you put a ring of white cement round the edge of the cover glass. This is easily done with the aid of a brass turn table sold for the purpose.
I think that by following these directions, and with a
little practice and delicacy of handling, some very fair slides may be turned out. You may, often, liowever, omit some portions of the process, and still make a very satisfactory examination of a rock. If you can manage to strike off a very thin flake about į inch across in the first instance, you can readily smooth down one side, attach it to the centre of a slip, and grind it down there till transparent, and it is at once ready for examination. A corundum file will be found very useful in rapidly rubbing down small specimens; plenty of water must be used with it to keep it cool, as also in all the grinding operations described above.
For grinding down the harder rocks, it will be advisable to use corundum in place of emery, except in the first operation. It can be had in three degrees of coarseness; but the two most useful for our purpose are “ medinın” and “ flour.” It can be got at the dealers in dentists' sundries.
In the case of a very friable rock it is advisable to soak it thoroughly in a solution of shel lac or spirits of wine, and let it dry and harden before rubbing it down; but in many cases such a rock can be readily examined after crumbling it by rubLing it in water with a brush, or crushing it gently with the fingers. The powder should then be dried, a small quantity laid on a slide ; drop a little benzine upon it, and then a drop of the thin balsam, and cover with a cover glass. For the examination of sandstones a freshly broken surface with a strong light thrown upon it will reveal most of its structure. But it can be reduced to sand as described above, and mounted dry, (do not attempt to examine it without mounting, or the grains of sand will probably do some injury to the microscope). A flat india rubber ring fastened to a slip makes a useful cell; lay the sand in this and cover with a thin cover glass; a little balsam round the edge will hold it securely. For grinding soft rocks, such as coal, a flat piece of pumice stone may be used with advantage. I have purposely said nothing about the use of the lapidary's wheel in this paper, as my object has been to shew how rocks can be prepared for examination by the aid of the most simple and readily obtained apparatus, by any practical geologist.
Field Meeting, July 7th, 1883. Held at Frodsham, Conducted by MR. CHARLES E. MILES. Good sections of the Waterstones and Lower Keuper Sandstone were seen. An
open fissure,” showing waterworn surface, was also noticed. In a quarry in the Building stones near Five-lane-ends, some examples of “ cracks” were found. Mr. T. MELLARD READE, F.G.S. directed attention to the occurrence of drift with boulders at a high level. At Dunsdale Hollow, the junction of the Keuper and Bunter rocks was observed.
Evening Field Meeting, July 13th, 1883. Held at the Dingle, Toxteth. Conducted by MR. G. H. MORTON, F.G.S. The fault in the Upper Bunter was inspected, and good examples of “ current-bedding” were seen. Mr. MORTON gave a very instructive address on the Ti sic formations occurring in the district, in the course of which he stated that several modifications of the original sub-divisions of the Trias, as laid down by Mr. E. Hull, F.G.S. of the Geol. Survey, and himself, were now found to be necessary, and pointed out that it was probable that all the rocks formerly classed as Lower Bunter either formed part of the overlying Pebble Beds, or else belonged to the Permian formation.
Evening Field Meeting, July 27th, 1883.
Held at Eastham. The junction between the Pebble Beds and (?) Lower Bunter was pointed out by Mr. G. H. MORTON, F.G.S., who gave some interesting remai on the rocks underlying the Pebble Beds in Lancashire and Cheshire.
EXCURSION TO SHROPSHIRE.
August 3rd to August 6th, 1883. The route included the country between Wenlock Edge and the Longmynd. DR. C. RICKETTS, F.G.S. conducted the party, which left Liverpool on Friday, August 3rd, and proceeded to Much Wenlock, where the Wenlock limestone quarries, rich in Corals and other remains of animal life in the Silurian period, were visited. At Rushbury, the remains of an interesting Roman Camp were inspected, and, at a little distance further on, the upper Llandovery Beds, with limestone containing the fossil Pentamerus were seen in the banks of a small stream. A section of metamor. phic rock on Cardington Hill was examined. At Soudley, near the picturesque village of Hope Bowdler, the quarries in the Caradoc sandstone yielded quantities of Cambrian fossils. Church Stretton was reached on Saturday night, and on Monday the ascent of the Longmynd was made, along the romantic gorge of the Carding Mill, by the Lightspout Waterfall. The Port Way (an ancient British track) having been reached, another valley was descended, leading to Little Stretton, where a fine section is exposed, showing the junction of the Llandovery conglomerates with the Longmynd rocks. After dinner at Church Stretton, in the evening, on the motion of the President, Mr. HENRY BRAMALL, M. Inst. C.E., a vote of thanks was passed to Dr. RICKETTS for his kindness in conducting the Excursion, and rendering so much valuable assistance.
Field Jeeting, August 25th, 1883. Held at Grimshaw. Conducted by MR, HENRY BPAMALI., M, Inst., C.E., President. A section of Gannister beds was inspecte i from above the railway cutting at Bimbo Lane Station. The nature of these beds, consisting of flagstones interspersed with shales, and containing but two workable seams of Coal, was explained. Gannister (which gives its name to the series) is the clay containing a large proportion of silica, which forms the base of the Coal seams. Fine sections in the Millstone Grit were seen at Houghton's Quarry and Grimshaw Delf. Specimens containing sulphate of baryta were found at the former quarry. The characteristic grit of the sandstone, caused by the decomposition of its felspar, was noticed in weathered specimens. In the banks of the Grimshaw brook, several exposures of Lower Bunter Sandstone were observed.
Ordinary Meeting, September 3rd, 1883. Held at the Free Library, Mr. HENRY BRAMALL,, M. Inst., C.E., President, in the chair.
The following were elected as members :
Messrs. J. Nicholls, T. Maguire, T. M. Jolmson, and the Rev. W. Paton.
Proposed as members :
Messrs. Edmund Rowe, 23, Frodsham Street, Tranmere; Charles Potter, 101, Miles Street; George Downie, 19, Oakfield Road; and Raoul James, 309, Upper Parliament Street, Liverpool.
AUDITORS. On the motion of Mr. Brennan, seconded by Mr. Rowland, it was resolved that Messrs. T. R. CONNELL and HOPKIN THOMAS be appointed Auditors for the Session.
DONATIONS. “ Transactions” Vol. II; “Report”, 1882, of the Liverpool Engineering Society ;
:-“ Proceedings” 1882-83, Liverpool Naturalists: Field Club; Ditto, Vol. I, Liverpool Astronomical Society ;-Ditto, Vol. 8, No. I, and • Report 1882, of the London Geologists' Association ; Report” 1882-83, Chester Society of Natural Science,--presented by the respective Societies ; The Mineral Resources of New Zealand," by Henry Bramall, M. Inst, C.E.,-presented by the Author ;-Ninth Annual Report on the Colonial Museum, Wellington, N. Z. by Dr. Hector ;-presented by Mr. Bramall. (Vol. III.-Session 1882-83.-No. 11.)