Sept. 4. 1879] 



NATURE 



431 



a portion (and it may be a diminutive quantity) locally detached 

 from the main stream, or a feeder dropping into the main stream 

 from steep, rocky sides. This is the primary cause. But along 

 with the presence of a graving machine in the falling waters, to 

 explain the making of the fonts a concurrent cause is necessary, 

 as otherwise they should be looked for anywhere and every- 

 where on rapid descents. The conducive condition is the coin- 

 cidence of falling waters with a veakn/ss of the rock, .nich as an 

 intersection of the division planes or fissures. I have secured a 

 specimen font, 10 inches deep and 12 inches width across the 

 bell-shaped mouth, in compact siliceous rock graven by a 



diminutive shoot of the main stream running down the depres- 

 sion which generally marks the edge of a division plane till it 

 reached an intersection ; at the intersection it graved a font, and 

 issuing from this went on to the next, and there graved another 

 (see sketch. Fig. i). The stream, flowing round and kept up by 

 a bed of rock dipping approximately in the direction of the 

 current, overflows in flood-time, or generally except in dry 

 summer weather, down the fissure A B ; at the intersections the 

 fonts were graven, and the water on leaving the lower one runs 

 along the edge of a superposed bed. We are now bound to seek a 

 limiting condition, as otherwise almost every pool into which there 



r.g.i 



is a waterfall might reasonably be expected to be a font. The 

 limiting cause is the relation between the size of the blocks into 

 which the rock is divided and the graving power of the falling 

 waters. If the waterfall is sufficient to grave a font of over a 

 certain size in rocks broken by planes into blocks of a certain 

 size, the consequence is that the whole blocks or blocks by frag- 

 ments will be broken away, and the walls will be the divisional 

 planes of the rock and lose altogether the font shape, as is wholly 

 or partially the case under our larger waterfalls owing to the 

 " pigmy plan" on which our (Slievardagh) rocks are broken up 

 by planes. Fig. 2 will explain the meaning I wish to convey. 



Suppose the rocks broken by two sets of planes, and there may 

 be many sets and the stratification as w ell ; now suppose a font 

 graven to the size of the circle ; it is plain that this could not 

 have stability, as the blocks at A, u, c, D would have come away 

 during the piocess. But had the font been so small as to take 

 only a portion of any four blocks no discontinuance of the graving 

 action could yet have occurred. 



I may add that about 2 feet in width and depth is the size of 

 the largest font I have come upon hitherto, 



William Morris 



Earlshill Colliery, Thurles 



The Good Time Begun 



The following has just been received from a nephew in the 

 Bombay Presidency, who, after speaking generally of a tremen- 

 dous gale from the south-west, with heavy sea, fog, &c., all along 

 the West Coast, writes thus more particularly : — 



" That same mist and rain have been for the present the 

 javing of this Presidency from another famine. It ('.he rain) 

 has been general and heavy all over the country, and was just in 

 time to save the crops, which were fast perishing from lack of 

 moisture. If we have a little more this month and another good 

 fall in September, we shall bo quite safe ; and I do trust we 

 shall not be disappointed, as another year — the fourth in succes- 

 sion—of scarcity would well nigh make 'the bankruptcy of 

 India,' so far as Bombay is concerned, a sad fact." 



You will note the appearance of this desiderated Indian rain 

 coming from the same direction as the chief part of that which 

 has been deluging our own country ; but which Mr. Campbell 

 shrewdly attributed, in Nature, vol. xx. p. 403, to the sun 

 recovering liis forces and beginning already to shine, after his 

 recent languid, sputless years, with increased radiation on the 

 great oceans of the south. PlAZZi SMYTH 



1 5, Koyal Terrace, Edinburgh, August 30 



Insect-Swarms 



T.s answer to Mr. Hawkshaw's question whether any one had 

 seen a flight of moths and butterflies in England similar to the 

 one he observed at Trouville on August 12 and 13, I can say 

 that on August 12 I was walking on the DawUsh Warren (a bar 

 of sand stretching across the moulh of the Exe) and noticed a 

 great number of P. gamma moths ; they were close to the edge 



of the water ; many of them were dead, and the sand hoppers 

 were eating them, but many more were alive and trying to flutter 

 inland, but seemed too weak to do so. I picked up some and 

 carried them to some wild thyme and they began to feed at once. 

 Some of the moths were in good condition but others very much 

 battered. The wind was blowing freshly from the sea at the 

 time. The moths swarmed in the hedges all the way from our 

 house to the Warren, a distance of four miles, especially on the 

 bramble flowers. There were a great many V. cardui with the 

 moths in the hedges, but none on the beach. A few days after- 

 wards I had a letter from my brother at Dieppe saying there had 

 been a swarm of moths and butterflies there, especially mention- 

 ins; i'- gamvia and V. cardui, but there were also skippers and 

 clouded whites. They swarmed about the town and countiy and 

 were lying dead on the beach. The swarm of moths and butter- 

 flics was also on August 12. EDITH I'YCROKT 

 Kenton, near Exeter, August 31 



Earthquake in Dominica 



A SEVERE shock of earthquake was felt here at 1.20 A.M. 

 yesterday (Sunday) the loth instant, and at intervals, until 1.52, 

 there were several tremulous movements of the earth. The 

 noise immediately preceding the first shock reminded me of the 

 clatter which is sometimes heard on board an oceangoing 

 steamer in very rough weather, when a heavy sea strikes the 

 ship, and all the crockery laid out for dinner is suddenly thrown 

 from the " fiddles " and broken into pieces on the floor of the 

 saloon. 



After the first shock there was an interval of perfect quiet 

 until 1.30, when subterranean noises like the discharging or 

 booming of distant guns attracted my attention, and then, at 



