33 6 



SCIENCE- G OSSIP. 



narrow disc, spot f.w. and a slight duskiness at the 

 out. marginal extremities of nervures in f. w. Second 

 subcostal nervule thrown off at the extreme end of 

 the cell. Neuration very conspicuous. U.S. with- 

 out yellow markings. Antennae long, with elongated 

 clubs. Only one species. 



i. A. erataegi L. Syst. Nat. i, p. 467 (1758). 

 Lg. B.E. p. 27, pi. 6, fig. 1, pi. 15, fig. 1. "The 

 black-veined white." 



46 — 62 mm. 



All the wings white, more or less sub-diaphanous, 

 more so in ? than in $ , without marginal fringe. 



Aporia erataegi. 



The neuration black. No markings either above or 

 below except sometimes a narrow disc, spot on f.w. 

 and some dusky triangular patches of scales along 

 out. marg. on f.w. at the extremity of the nervules. 

 Antennae, head, thorax, and abdomen black. Body 

 slightly downy. U.S. as above. 



IIab. The entire Palaearctic Region, except N. 

 Lapland, Syria, and the North American portion. A 

 very common insect in many parts of Central Europe. 



V VI. Rare and local in England, once common, 



but now only found in Kent. 



Larva. Covered with a white down, sides and 

 ventral surface lead-coloured. Dorsal surface marked 

 with two longitudinal yellowish bands. Feeds gre- 

 gariously on hawthorn (Crataegus), sloe and wild 

 cherry [Primus), and other fruit trees. IV.-V. 



Pupa. Greenish-white, with two lateral lines of a 

 yellow colour, and with numerous black points. 



(To be continued.) 



To Clean Coral. — Cut some common brown or 

 "Sunlight" soap into thin slices, and boil till dis- 

 solved. Then fill a larger saucepan so as to cover 

 the coral with water, and add the dissolved soap with 

 some washing soda. Place the coral so that the dirt 

 will fall out of, not into the recesses of the specimen, 

 and boil for ten minutes. Then rinse in clean hot 

 water, finishing with cold water. Euplectella may be 

 cleaned by simply dipping into the boiling water and 

 rinsing in clean warm water. The amount of soap 

 and soda, and the time of boiling, must be judged by 

 the circumstances. I have found coral well cleaned 

 with a few minutes' boiling, or it may be boiled for an 

 hour without injury. — E. Barker, 41 Melrose Gardens, 

 London, IV, 



A HISTORY OF CHALK. 



By Edward A. Martin, F.G.S. 

 {Continued from page 307.) 



T^HE Upper Cretaceous sea had a considerably 

 wider extension than that of the Lower Creta- 

 ceous or Neocomian period. In the Weald en area we 

 find the various subdivisions of the lower portion of 

 the system recurring with regularity, one above the 

 other ; but, in consequence of the widening of the 

 sea, the deposits laid down in the later beds came 

 to overlap the earlier beds. Thus the extreme 

 westerly outliers of the Upper Greensand occur upon 

 Triassic strata in Devonshire, while the Gault where 

 it outcrops west of the great escarpment occurs 

 unconformably upon the later members of the 

 Jurassic, as far as the outcrop of the Kimmeridge 

 Clay. 



Where the Gault and Upper Greensand occur in 

 superposition we have good evidence of their de- 

 position having taken place in undisturbed succession. 

 There is no great break shown in an examination of 

 their fossil contents, the differences being such as 

 might be expected from the different nature of their 

 lithological characters. The Gault Clay was un- 

 doubtedly brought together by a process of calm 

 undisturbed deposition far out at sea, and at such a 

 distance from land as to render it impossible for the 

 ordinary sandy waste and debris of a coast to have 

 been transported thither. Only the finer clay was 

 borne, finally to sink to rest at the bottom of the sea, 

 entombing many representatives of the pelagic life of 

 the period. The lower portions of the rock are espe- 

 cially rich in fossil remains, and show that it was 

 formed in a sea which was gradually deepening. The 

 Clay, where it occurs in its pure recognisable form, is 

 of a dark blue-grey tint, and contains many mica- 

 flakes. In some localities, such as at East Wear 

 Bay, near Folkestone, there is a large amount of 

 iron-pyrites contained in the Lower Gault. The Upper 

 Gault here develops grey marly beds, indicating a 

 deepening of the sea in which they were deposited. 

 Layers of concretions of phosphate of lime also occur. 

 The thickness of the Gault varies considerably at 

 different points. The most reliable information on 

 this head has been obtained from borings which have 

 been made in the London basin in search of w : ater, 

 the thickness in these cases being as follows : — 

 Tottenham Court Road, 160 feet ; Crossness (Black- 

 wall), 176 feet; Ware (Herts), 160 feet; Turnford 

 (Cheshunt), 164 feet; Kentish Town, 130.; feet; 

 Richmond (Surrey), 201^ feet ; Chatham Dockyard, 

 193 feet; Streatham, 188 feet; Dover Convict 

 Prison, 143 feet ; Farnham Waterworks, 152 feet ; 

 Caterham Waterworks, 343 feet ; Culford (Eastern 

 Counties Coal-boring Association), 49! feet. It 

 must, however, be remembered, in connection with 

 measurements of thicknesses obtained from borings, 

 that they are vertical plumb-line measurements, 

 and are not necessarily measured at right angles to 



