Correspondence — Mr. A. Harker. 479 



coi^E-iEsiPon^zDiEisroE. 



PACKING OF SAND GRAINS. 



Sir, — Since the appearance of Mr. Mellard Eeade's letter (p. 288), 

 I have made some experiments, the results of which may be woi'th 

 recording. The process followed was to take a specific gravity bottle 

 of capacity 50 cubic centimetres, fill with sand, place in a balance 

 and carefully counterpoise ; then fill with water and from the in- 

 crease of weight deduce the amount of water taken in. This 

 method is sufficiently exact, and requires only one weighing, and no 

 estimate of specific gravity. The sand was packed by continual 

 shaking, not j)ressing, and it decreased in bulk very considerably 

 during the process. Coarse brown sand was found to occupy -TlGo 

 of the whole volume of the bottle, while fine sand filled -7362 of 

 the space : these results are very little short of the calculated figure 

 for " pyramidal order," -7405, and would doubtless be still closer if 

 the sand were packed wet and with the aid of pressure. Against the 

 sides of the vessel there is a necessary departure from the close order 

 which obtains in the interior, and this disturbing element becomes, 

 of course, more marked in proportion as the size of the grains com- 

 pared with that of the vessel is larger. Thus in the same vessel 

 fine sand packs more closely than coarse, and to obtain a similar 

 approximation to pyramidal order in the case of shot would require 

 a vessel of very considerable dimensions, much larger than Mr. 

 Eeade's rain-gauge measurer. 



Nantlle, July ld,th, 1884. A. Hakker. 



PEOF. BONNEY, F.E.S., AND MR. J. H. COLLINS, F.G.S., ON THE 

 SERPENTINE OF THE LIZARD DISl'RICT. 



Sir, — In the Quarterly Journal of the Geological Society of August 

 1st, Mr. Collins in his paper " On the Serpentine and Associated 

 Eocks of Porthalla Cove," has called in question in a very decided 

 manner the igneous origin and intrusive nature of the serpentine of 

 that district — views held by Prof. Bonney and urged by him in 

 several papers printed in previous issues of the same journal. 



Mr. Collins contends " that the hornblende schist, Serpentine, and 

 other rocks described are distinctly interstratified, and that there is 

 a real passage from one to the other," that the whole "consists of 

 stratified rocljs altered in situ by a kind of selective metamorphism." 



As an independent observer, and as one who has had many 

 opportunities of studying the subject in the locality referred to, I 

 feel desirous, in the cause of what is right, of confirming Professor 

 Bonney's views as to the true igneous and intrusive character of the 

 serpentine, of which very fortunately there is quite an abundance of 

 evidence, and not by any means a mere matter of opinion. 



From Porthalla Mr. Collins has drawn most of his arguments in 

 favour of his views, but here there are the most convincing proofs of 

 the intrusion of the serpentine among the hornblende slates, even 

 more decided than any other examples I have yet seen in the Lizard 

 district. In several of the sections here exposed the serpentine is 



