380 Reports and Proceedings—Mineralogical Society. 
their elasticity, so as to resume as far as possible their original relation to the 
rock-masses with which they are still connected. This movement of release may 
give rise to two kinds of periodic disturbance : 
(5) short-period vibrations, due to a sudden arrest by an obstacle and 
constituting the earthquake properly so called, and 
(6) a slower backward and forward swing of the rock about the position of 
equilibrium. 
The more important permanent variations in the configuration of 
the earth’s crust in the neighbourhood of the San Andreas fault in the 
Californian earthquake of 1906 are well shown by the model. This 
earthquake is regarded as an incident in the slow northward creep of 
the North Pacific relatively to the adjoining continents, part of the 
process of adjustment of the earth’s crust to the interior—rendered 
necessary by the expansion of the crystalline rocks of the former on 
hydration, and the contraction of the latter as the result of cooling 
and loss of material by volcanic and kindred phenomena. 
The President read the following communication received from 
Mr. S. 8. Bucxman, F.G.S. :— 
May 29, 1910. 
‘Tn my paper on certain Jurassic Species of Ammonites (Quart. Journ. Geol. Soc., 
1910, vol. lxvi, p. 90). 1 proposed for a new genus the name Burtonia (p.97). With 
that kind helpfulness which is so distinctive of American scientific workers, Dr. W. H. 
Dall writes to say that this name is already in use—by Bonaparte for a bird and by 
Bouvignat for a naiad. I therefore desire to substitute the name Bredyia for 
Burtonia in my paper; Bredyia is from the River Bredy (pronounced ‘ Breedy’, 
‘ Briddy’), which flows through Burton Bradstock, and its name presumably furnishes 
the syllable ‘ Brad’. I wish to record my thanks to Dr. Dall for his kindness. 
‘« The opportunity may be taken to rectify a misprint: in p. 68, 1. 7 from the top, 
for ‘ striking ’ read ‘ sticking’.”’ 
II.—MrveratoaicaL Soctery. 
June 7, 1910.—Professor W. J. Lewis, F.R.S., President, in the Chair. 
_ Arthur Russell: On the occurrence of Phenakite in Cornwall. 
Phenakite was unknown in the British Isles until the discovery by 
the author in 1905 of a single specimen at the Cheesewring Quarry, 
Linkinhorne, Cornwall. In 1906 he collected further specimens, 
showing numerous small but well-formed crystals, from a tin lode 
at South Phoenix Mine, Linkinhorne. In an old Cornish collection 
acquired by him in 1909 he found a specimen with as many as forty 
fine crystals; it was labelled “Topaz on Quartz from St. Agnes”’. 
Phenakite was also recognized on a specimen found about the year 
1870 by Mr, J. H. Collins at South Crofty Mine, Illogan, Cornwall. 
Search at the Natural History Museum and the Museum of Practical 
Geology brought to light other specimens of phenakite placed under 
apatite.—Dr. G. F. H. Smith: (1) Phacolite from near Belfast. Two 
types were described. In the first the crystals were large (about 
10-14 mm. across) and much striated, and in the second they were 
small (about 1-2 mm. across) but with plane faces; in both instances 
the crystals were twinned about the trigonal axis, the individuals 
interpenetrating one another, and the forms present were r (1011), 
t (8142), e (0112), s (0221). The measurements accord closely with 
the data given for chabazite. (2) The Crystalline Form of Nitrogen 
