HARD WICKE 'S S CIENCE - G O SSIP. 



75 



to crystallize, although it is that one which is the 

 most difficult to fuse, and which [would therefore 

 naturally be expected to have been solidified before 

 the felspar and the mica. But it has been sliown that 

 when quartz is in combination with other mineral 

 substances, it is often as readily fusible as they are ; 

 and thus what must be called accidental circumstances 

 may have led, in the case of the rocks in question, to 

 its being crystallized after the felspar, which we so 

 generally find to have modified tlie form of the 

 quartz ; this latter appearing as a glassy paste in- 

 closing the accompanying minerals, instead of having 

 a definite form of its own. It has also been ob- 

 served that the felspar in solidifying would liberate a 

 sufficient quantity of heat to enable the quartz to re- 

 tain its viscous state (Durocher) ; just as, on the other 

 hand, in the quartz porphyries we see an instance of 

 the analogous effect of the crystallizing quartz upon 

 the felspar. It is asked how the enormous masses 

 of quartz which form some of the schistose rocks can 

 have been produced ? We must appeal to metamor- 

 phism. The contact of highly-heated eruptive matter 

 might thus alter a quartz or sandstone into an almost 

 pure quartz rock. Heat and pressure combined are 

 mighty agents, which might also effect a similar 

 change during the course of long ages. 



That water at a high temperature can hold quartz 

 in solution is well illustrated by the deposits of sili- 

 cious sinter, thrown down by thermal springs, as, for 

 instance, the Geysers of Iceland, and by others in 

 Kamtschatka and in New Zealand : this silica often 

 encrusts mosses and other substances in the same way 

 that we may see calc-tuff forming petrifactions in 

 other localities. The delicate feathery crystallizations 

 of silicious sinter are extremely beautiful. 



The quartz of veins appears generally to have been 

 deposited from aqueous solution, and will be seen, as 

 has been already remarked, to contain innumerable 

 cavities inclosing water. Occasionally these watery 

 cavities are of large size, and may be observed with- 

 out any instnimental aid. 



(71; be continued.) 



THE ENTOMOLOGY OF EPPING 

 FOREST. 



EPPING FOREST, being a large tract of beauti- 

 ful woodland, affords ample scope for pleasure 

 and recreation to the lover of nature ; no matter 

 whether a collector of fungi, a botanist, an ornitholo- 

 gist, or entomologist, or naturalist in any shape or 

 form : here is situated, as if for the special benefit of the 

 inhabitants of this great metropolis, a beautiful re- 

 creation-ground, in which each can carry on the par- 

 ticular branch of Natural History in which he takes 

 the greatest delight. 



To the entomologist, Epping Forest seems to have 



a special charm, the glades in the neighbourhood of 

 Servardstone and High Beech being both fiill of good 

 sport and sylvan beauty. Let us commence our 

 rambles in the old forest in the month of April. The 

 scene of our sport shall be Chincford, and that em- 

 barrassing little insect Pidaria the chief object of it. 

 It is just getting dark, and as much as we can do to 

 keep our feet out of the little rivulets or brooks which 

 are continually coming in our way ; but, lighting our 

 lanterns, which are a great boon for other than ento- 

 mological purposes, we proceed to examine the blos- 

 soms of the Sloe. We are fortunate enough to obtain 

 a few of this local insect, whilst flying about are 

 Geometers, Badiafa, Sitffitmata, and Ilhaiai-ia, and 

 on sallows in the neighbourhood, Noctuas, Cruda, 

 Gothica, Instabilis, Rubrkosa, and Lithorhiza. In 

 the month of May, when every hedge is showing itself 

 off to its best, and when the air is teeming with in- 

 sect life, we may with great pleasure take another 

 ramble in the same locality. At Fairmeads Plain, 

 High Beech, we shall be delighted to see flying here 

 and there over the bracken that pretty little fritillary, 

 A. Eiiphrosynic, and later on in the month, Selene, 

 the small pearl-bordered fritillary, but not so plenti- 

 fully as her twin sister. In meadows adjoining, and 

 on the outskirts, we may count on getting Carda- 

 mines, Argiolns, Tages, and most of the common 

 butterflies out this month ; and we may also come 

 across the half-noctuas Mi and Glyphica, together 

 with those pretty Geometers Jacobcca and Mac2ilata, 

 and flying about in the sunshine two of the Hooktips, 

 Hamnla and Falcula. On a bright day in this month 

 we shall not return home with empty boxes, and 

 shall have had quite enough to do to set our 

 captures. 



The beginning of June is the best time for larva- 

 beating. In the first week we may expect to obtain 

 by beating the Oak the larva of Tliecla Quereus, and 

 shall by this means be able to procure a far more 

 beautiful and perfect series for our cabinets than by 

 the most careful selection from those obtained on the 

 wing. On blackthorn, Cczndeocephala (very plenti- 

 ful), B. CratiEgi, and Quereus, together with Thecla 

 Betiiltc, will reward the perseverance of the col- 

 lector. In the evening, we may get by dusking, 

 in the neighbourhood of Walthamstow, Geometers, 

 Petraria, Obliquaria, perhaps Papilionaria, and 

 Russata ; and among the Cuspidates, Spinula and 

 Cainelina ; whilst on sugar Batis and Berasa are 

 beginning to appear, together with Trilinea, Psi, 

 Plecfa, and hybernated specimens of Libatrix. By 

 beating the bushes in the daytime, Temerata, the 

 Clouded Silver, will reward our exertions, and not 

 unlikely Ptmctaria, Atomaria, and Prunaria will 

 come across our path. 



July brings many fresh moths and butterflies with 

 us. In the neighbourhood of oak-trees we shall see 

 Thecla Quereus, giving us a glimpse now and then of 

 his rich purple colours ; but we shall not obtain many 



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