HARDWICKE'S SCIENCE-GOSSIP. 



221 



to the presence of the other oxides, There is also a 

 large quantity of a black mineral in small amorphous 

 fragments with a semi-metallic lustre, and whose 

 density appears to be about five. It is not easy to 

 apply a specific name to the mineral substance of 

 which these fragments must have formed part, but they 

 contain oxides of iron and manganese, and another 

 reaction is given which would appear to indicate the 

 presence of tin, a not improbable assumption, con- 

 sidering the proximity in the neighbourhood of 

 granitic rock with which that metal is often associated. 

 There are some small particles of an olive-green 

 colour, and appearing translucent, but they are so 

 few, and their size is so minute that it is impossible 

 to approximate with accuracy to their density, unless 

 in a chemical balance of the finest construction, but 

 it is just possible they may belong to the class of 

 minerals known as olivines. These, however, are 

 much more abundant in the neighbourhood of basalts 

 or augitic lavas, and on the north-east coast of 

 Ireland, they form a considerable part of the sands. 

 Beside these olive-coloured particles there are a few 

 isolated fragments of a brighter tint, approaching 

 that of the emerald, and also translucent, which 

 would appear to be small pieces of apatite. Density 

 and streak being difficult to ascertain with such very 

 minute particles one cannot do more than surmise 

 the presence of the mineral, judging from the greenish 

 coloration of the flame obtained with sulphuric acid. 

 It is, however, quite possible that a few might be 

 minute pieces of beryl detached from a larger mass. 



There are other stones of a dull greenish colour 

 scattered abundantly through this sand, though dis- 

 tinct in appearance from the supposed olivines or 

 apatites. They would appear to belong to the rock 

 known as greenstone porphyry. Many large masses 

 of this substance, more or less rounded by attrition, 

 may be found on the strand at Bray, a! mile or two 

 off, where a number of interesting stones may be seen 

 at any time thrown into bands of various sizes. It 

 may be stated that the island of Lambay, lying to the 

 north of Dublin Bay, is known to consist in a great 

 measure of greenstone porphyry, which would tend to 

 warrant the conclusion as to these fragments. It need 

 hardly be stated, that none of the minerals last de- 

 scribed give any reaction with hydrochloric acid, but in 

 nearly all of them there is distinct effervescence, when 

 fused with carbonate of soda on charcoal, shewing 

 them to be silicates, whilst the reaction for iron, 

 whether in the state of protoxide or sesquioxide is 

 well defined. 



Space will not permit of all the various minerals 

 appearing in the sand being enumerated, but one or 

 two others may be briefly referred to. In turning 

 over the siliceous particles, a number of transparent 

 globules distinctly rounded, and having a peculiar 

 pearly lustre, appeared amongst the darker portions. 

 They were different in form from the silica before 

 referred to which was amorphous, and the probability 



of their being topaz might at first be suggested. 

 However, on picking out a sufficient number to de- 

 termine the specific gravity, it was found after careful 

 experiment to be 2 • 4, and as they gave no reaction 

 with the blow-pipe beyond that for silica, it is pro- 

 bable they may belong to the opal group, and be 

 classed as hyaline quartz. They were certainly in- 

 ferior in hardness and density to the quartz usually 

 found in abundance in every description of sand. A 

 few isolated masses of a dark red colour subtranslu- 

 cent and with a vitreous lustre also occurred, and 

 were at first somewhat likely to be confounded with 

 the essonites. They were, however, without crystal- 

 line form, and on testing with soda on platinum foil, 

 a yellowish colour appeared, indicating chromium, 

 from which it would probably not be far from the 

 truth to consider them as pyropes, or garnets of the 

 magnesia-alumina class, which often shew this 

 reaction. 



When the nature of sand is taken into consideration 

 and the difficulty of discriminating correctly as to 

 form and colour in very minute bodies, it will be seen 

 that a description of any kind of sand which has un- 

 dergone the process above described, must be made 

 with more or less uncertainty. The subject, however, 

 is well worthy the attention of students, as shewing 

 more accurately the constituent elements of rocks, 

 particularly those which appear near the coast. I 

 purpose, however, making experiments on other sands 

 on different parts of the coast in this county during 

 the coming season. 



W. McC. O'Neill. 



Dublin. 



DREDGING IN THE FRITH OF FORTH. 

 By S. P. Alexander. 



{C oniinued front j>age 202.) 



SUCH then, are a few of the principal specimens 

 obtained by the dredge, at this depth. Let us 

 see what can be brought up from still greater depths. 

 We throw in our net again, at a distance of two 

 hundred yards or so, out from the Gantocks yonder. 



Here the depth is about twenty fathoms, so we let 

 out forty fathoms of rope. At this depth, and with 

 such a length of rope, one cannot propel a rowing- 

 boat very far. If in a sailing-boat, however, we will 

 do more execution. When the dredge is brought up, 

 perhaps^our attention is at once'riveted by a reddish- 

 yellow object hopping about at a great rate in the 

 bottom of the net. When examining this more 

 closely, we see a delicate yellow fleshy substance 

 covered with scarlet spots ; and, protruding from it, 

 long delicate pink filaments rapidly twining about, 

 like those hair worms (Gordius) most of us have 

 noticed in fresh water. 



This lovely object, which at first glance is puzzling, 

 is the cloaklet anemone {Adanisia palliata) adhering 



