HARDWICKE'S SCIENCE-GOSSIP. 



some cases, such as the granite used for building pur- 

 poses about Dublin, the decomposition being very 

 rapid. The decay appears to me to be due to the 

 state of agglomeration of the grains of which it is 

 composed, in addition to the chemical nature of its 

 constituent minerals. Solid granite rocks decay in 

 situ to the depth of many feet, and the resultant of 

 the decomposition is, in Cornwall, kaolin or china 

 clay. In the boulder clay about Liverpool, we find 

 many decayed boulders of granite and greenstone, in 

 some cases the core being preserved, and ringing like 

 metal under the hammer, while the surface exfoliates 

 and falls to powder. Limestone appears to be beauti- 

 fully preserved in the clay, but exposed to the atmo- 

 sphere it is dissolved away. These specimens show, 

 in the case of limestone, the most delicate striations 

 preserved, in the case of greenstone only a resultant 

 powder. 



If from such small examples we extend our views 

 to natural scenery, we find that its character has been 

 largely determined by chemical action. The valleys 

 and dells of Derbyshire, so admired for their beauty, 

 the gorge of the Chee Tor, the cliffs of Cheddar, in 

 Somersetshire, all result from the dissolution of lime- 

 stone by the chemical action of rain, but by far the 

 most remarkable features of limestone districts are the 

 caverns with which they abound. The Peak Cavern, 

 Kent's Hole, Wokey Hole, the Mammoth Cave of 

 Kentucky, are all produced by the continued action 

 of water percolating from the surface through joints 

 and fissures, removing the lime in solution, and en- 

 larging, slowly but surely, its channels until large 

 caverns are produced, sometimes underground rivers, 

 and, finally, as the roof falls in, valleys. 



Having just returned from a visit to the Burren, a 

 remarkable limestone district in county Clare, by 

 Galway Bay, I was much struck with the effect of 

 chemical action on the scenery. There you have 

 grand limestone mountains, rising terrace above ter- 

 race, in many places entirely bare of verdure, in 

 others covered with grass, of the hue which gives the 

 name of the "Emerald Isle" to Ireland, while a 

 closer inspection shows most of the terraces and the 

 sides of the mountains to be split up with joints in 

 all stages of enlargement by rain wash, the upper sur- 

 faces often bare ; in others with basin-shaped hollows 

 holding water like a saucer, in which a fresh-water 

 Alga grows. In others the joints may be overgrown 

 with moss and verdure, giving a treacherous appear- 

 ance of solidity — places to be avoided at the risk of a 

 sprained ankle or broken leg — but by far the most 

 curious thing is to see, perhaps 18 inches down at the 

 bottom of the crevices, the surface rocks being bare, 

 ferns growing in the greatest luxuriance. My friend, 

 Dr. King, of Galway, pointed out to me that the 

 decay of the Alga formed a very fine soil which washed 

 into these crevices, forming a fitting support to the 

 Maidenhair fern. The Alpine plant, Dryas octopetala, 

 also grows in great luxuriance, and is the relict of a 



former Arctic climate. In other places, where the 

 rock is not "jointed," Dr. King informs me, there 

 exist plains of bare limestone. Not a stream of 

 water is to be seen in all this remarkable district, but 

 many springs, which the inhabitants hold in super- 

 stitious reverence, and call "holy wells," sometimes 

 forming very picturesque subjects for sketching ; of 

 this character is the one at Glen Inah, near Bally- 

 vaughan. This continual solvent action on the rocks 

 from the joints frequently quarries out large blocks of 

 limestone, proving, I have no doubt, of great advan- 

 tage to the builders of those remarkable structures 

 called "Round Towers," the objects of so much con- 

 troversy and little knowledge, of which the use has 

 never been discovered, nor the date of their building 

 fixed. 



Lochs Mask and Corrib are both basins in the 

 mountain limestone of Connemara. They communi- 

 cate only by an underground river. To show the 

 necessity of a knowledge of geology to the engineer, 

 I may mention that during the famine an attempt was 

 made to cut a canal to connect the two lakes for 

 navigation purposes. The cut was made, but when 

 the water was turned in, so fractured and fissured were 

 the bottom and sides that the canal would not hold 

 water, and it remains to this day a monument of 

 misdirected energy. 



To treat fully of the connection between scenery 

 and chemical action would take up more space than I 

 have at my disposal, but I trust in this short outline 

 I have given an insight into the forces which produce 

 natural beauties that charm the eye, or grander ones 

 that awe the mind. The forces of the storm-tossed 

 sea, the hurricane, the earthquake, and volcano, may 

 seem much more potent and terrible, but the ever 

 evenly enduring wear of the elements through chemical 

 action produces in the end results quite as great, nay, 

 greater, though it is so distributed and slow as to be 

 unappreciable to the eye except in its effects after 

 long lapses of time. 



ON THE DEVELOPMENT OF THE HOUSE- 

 FLY AND ITS PARASITE. 



THE following remarks on the development of the 

 house-fly are such as have come under actual 

 observation, and the appended sketches were made by 

 Mr. G. Harkus from the microscope, with the aid of a 

 Beales reflector. 



Mr. Harkus, with whom I experimented simul- 

 taneously, was fortunate, or the reverse, in having the 

 required ova brought to him in this way. A fly having 

 gained access to a cold joint of lamb considerately 

 left a sufficient supply for his examination. The 

 objectionable part of the arrangement was probably 

 counterbalanced by his being enabled to fix the time 

 of deposition with tolerable certainty. This was on 

 July 28. The eggs (one of which is represented 



