q 



48 PROCEEDINGS OF THE 



The thanks of the meeting were voted to Mr. Draper for his 

 papers. 



Mr. W. R. Traviss exhibited under microscopes two fragments 

 of quartz crystals. Referring to one of the mounts, he said it 

 showed a series of seven faint lines across the field, parallel, but 

 not equally spaced. He suggested that the lines at one time 

 were respectively the outer surfaces of the crystal. The plane 

 of this particular surface in the mount referred to was at right 

 angles to the plane of the microscope stage, so that by focusing 

 down one could look along this plane. It was then noted that 

 this " old crystal surface " was covered with a number of very 

 small crystals, or debris, which had been deposited on this plane. 

 Presently the crystal went on growing, and again a period of rest 

 and more debris deposited or formed. This was repeated seven 

 times, but the exterior face was quite smooth. 



Then as to the occasional presence of contained bubbles of 

 liquid in quartz (and other) crystals. It was suggested that it 

 was possible that they were formed by a bubble of gas adhering 

 to perhaps the under surface of a growing crystal, and material 

 being deposited round and over it. 



Some discussion followed on liquid enclosures in crystals and 

 the nature and method of identification of the gases contained. 

 The chairman drew attention to a paper by Mr. Ashe on the 

 effects of temperature on enclosed liquids. (Journ. Q. M. C, Ser. 

 2, Vol. VIII., pp. 545-8, pi. 28.) 



Mr. E. M. Nelson sent a note on a peculiar form of diatom. 

 During an examination with dark-ground illumination of Mr. 

 Siddall's filaments on some Coscinodisci in a diatom gathering, 

 mounted and kindly given me by Mr. Chaffey, a small portion 

 of sandy grit was found to have similar filaments protruding from 

 it. Its colour was a golden yellow, the same as the sandy grit 

 usually seen in this kind of slide, which contains diatoms mounted 

 in sea-water in their natural state. The dark-ground illumi- 

 nator was removed, and when the object was examined by an 

 oil-immersion gth with transmitted light from an achromatic 

 condenser, the green chlorophyll pustules of a diatom could just 

 be made out inside the conglomerated mass of sandy grit. A 

 search was then made over the slide, and three or four other 

 similar specimens were found. So it appears, then, that there is 

 a " caddis-worm " form of a diatom. What species this diatom 



