HARD WICKE'S SCIENCE- G OSS IF. 



147 



material, but usually a caustic alkali is necessary to 

 effect it : this requires great care in using, as silica 

 is soluble in potash or soda. I usually add the caustic 

 to the water and deposit whilst boiling : in the course 

 of a few seconds the material begins to break up. 

 The contents of the test-tube should now be poured 

 into a precipitating glass three parts filled with water 

 (ordinary water will do) ; after subsidence, the water 

 must be poured off, and the deposit returned to the 

 test-tube (which should be three parts filled with 

 water), and then vigorously shaken. If, as is fre- 

 quently the case, some of the material still remain 

 unbroken, a further boil in caustic will be necessary. 



The sub-peat deposits generally yield to a weak 

 solution of bicarbonate of soda : they should after- 

 wards be boiled in nitric acid. 



The final treatment with liquor ammonite should 

 never be omitted : those who have never before tried 

 it will be astonished at the freedom from flocculent 

 matter, and the brilliancy of the diatoms. 



In concluding these instructions, I must urge 

 all those who wish to make good slides to use the 

 purest distilled water obtainable, and to make sure 

 that no traces of the acids or alkalies used in cleaning 

 have been retained. I must also caution the learner 

 against a plan proposed in some books on the pre- 

 paration of microscopic objects, viz., burning the 

 vegetable and animal matter away by heating on a 

 platinum spoon. This is utter destruction to the 

 diatoms. 



In a future number I hope to describe my plan of 

 selecting and mounting. 



THE UNDERGROUND GEOLOGV OF 

 LONDON. 



THE ultimate conclusions based upon the results 

 of the deep boring at Messrs. Meux's breweiy, 

 Tottenham Court-road, have been singularly confirma- 

 tive of geological predictions. We referred to these 

 in our last number, and pointed out, what were for a 

 few days believed to be differences of opinion, 

 although we were strongly inclined to believe that 

 Mr. Godwin-Austin's general theory would ultimately 

 prove true : such has been proved to be the case. 

 Many years ago the above eminent geologist pointed 

 out that the rocks which came up in Somersetshire on 

 the west, and formed hilly ground there, and which, 

 beyond the south-eastern side of England, on the 

 Continent, formed the high ground of the Ardennes, 

 must strike across England in the vicinity of London. 

 Thereabouts this chain of hills must be let do\ATi, and 

 over the tops of the hills other deposits of later date 

 must have accumulated and masked them. Messrs. 

 Meux's hope in going on with their deep boring, was 

 to find the Lower Greensand formation, where they 

 would secure plenty of good water. At first, after the 

 London clay and upper chalk had been passed through, 



it was thought that this formation had been struck 

 upon. Such an event would have been good news 

 for the metropolis. Instead of this, however, it now 

 turns out that the bed, which it was thought might be 

 one of the Greensand strata, is only the old, weathered, 

 superficial upper surfaces of a deposit, geologically 

 speaking, much older. After the borer had passed 

 through a few feet of this, it suddenly entered green 

 and purple-coloured slates, having an appearance 

 which geologists are in the habit of associating with 

 the Primary rocks. It will be remembered that Mr. 

 Godwin-Austin held that the old ridge of rocks lying 

 at no great depth underneath London would be found 

 to be of Primary or Palceozoic age, and possibly 

 belonging to the Carboniferous formation. A well- 

 boring, carried on some years after this theory was 

 propounded, at Kentish Town, actually sti'uck on the 

 old ridge, although the cores brought up were not 

 scientifically satisfactoi-y in determining the geological 

 age of the rocks thus reached. Afterwards, in a deep 

 well-boring at Harwich, underneath the chalk, similar 

 old rocks were pierced at a depth of a little over 

 1,100 feet, and here the Lower Carboniferous rocks 

 were reached, as was evident from one characteristic 

 Lower Carboniferous fossil brought up in the lowest 

 cores of rock. 



These two facts, so strangely confirmatory of a 

 bold geological theory, have caused geologists to be 

 on the look-out for deep-well or other borings in and 

 about London. They had no small influence in bring- 

 ing about the sub-Wealden explorations in Sussex. 

 The green and purple slates brought up a few days 

 ago from beneath Tottenham Court-road, were found 

 to be highly inclined, at an angle of about 30 degrees 

 dip. Unfortunately the boring tool which brought 

 up a specimen of these highly-inclined slates, had to 

 be turned round many times before it came to the 

 surface. Hence we are completely in the dark as to 

 the direction of the dip. If this.could be ascertained, 

 it would be no difficult task to calculate how far we 

 should have to go, on the south and north of this sub- 

 terranean mountain axis, before we should bore for 

 coal with any possibility of success. The purplish 

 green slates found underneath Tottenham Court-road 

 are said strongly to resemble the rocks found at the 

 bottom of the deep well-boring at Kentish Town, 

 The cores containing these slates were confided to 

 Mr. Robert Etheridge, F.R.S., palseontologist to the 

 Geological Survey, who immediately discovered, from 

 the nature of the fossils imbedded in them, that they 

 were of Devonian, or Old Red Sandstone age ; and 

 they are said to be almost identical with the rocks of 

 the Eifel. The most characteristic fossils found in the 

 cores were Spirifera disjuncta (formerly called Spi7-i- 

 fera Verneuilli, a characteristic Devonian fossil on the 

 Continent), and Rhynchonella aiboides. 



We here obtain a glance at the vastness of the 

 physical changes which must have taken place under- 

 neath us. These Devonian rocks were formed along 



H 2 



