On the Wood's Point Dyke. 517 



a detailed investigation desirable. With a few exceptions, the 

 earthquakes originated beneath the district lying between Inverness 

 and the north-eastern end of Loch Ness. The mean direction of the 

 fault, which follows the line of the Great Glen, is jST. 35° E. and 

 S. 35° W. and its hade is to the south-east. The isoseismal 8 con- 

 tains 67 square miles, and its centre is about 1| miles east -north-east 

 of Dochgarroch and f mile south-east of the fault-line. The corre- 

 spondence between the position of the great boundary-fault and of the 

 fault inferred from the seismic evidence is so close, that there can be 

 little doubt that the earthquake was due to a slip along this fault. 



The nature of the shock, the sound-phenomena, time-relations, and 

 after-shocks are described in detail, and some account is added of 

 the earthquakes of 1890 and of sympathetic earthquakes in the 

 valley of the Findhorn. There were two distinct slips in rapid 

 succession, with continuous slight motion between them, the second 

 being greater in amount and extending over an area which probably 

 overlapped, even if it did not entirely include, that within which 

 the first took place. The great slip reached nearly from Loch Xess 

 to Inverness, and was greatest at a point about half-way between. 

 The three chief after- slips resulted in an extension of this area in 

 both directions along the fault-surface, the extension to the north- 

 east being small, while that to the south-west amounted to 6 miles 

 or more. In addition to this migration of the focus, there was also 

 a continuous decrease in the depth of the focus. The earthquakes 

 provide no evidence with regard to the direction of displacement 

 along the boundary-fault. There can be little doubt, however, that 

 Loch Ness is still growing ; but it can hardly be determined whether 

 the lake is now contracting in area, or whether it is gradually 

 pushing its way outward to the sea. 



3. ' The Wood's Point Dyke, Victoria (Australia).' By Frederic 

 Philip Mennell, Esq., F.G.S. 



This dyke is intrusive into a belt of Silurian (Upper Silurian) 

 strata which strike in a direction somewhat west of north, and 

 extend beyond Walhalla on the south. Wood's Point is about 

 75 miles east of Melbourne. It may be taken as typical of the 

 intrusions associated with the Silurian rocks of the Victorian gold- 

 fields. Brown, original, hornblende is the dominant constituent, but 

 it is rarely idiomorphic ; augite, three varieties of felspar, micro- 

 pegmatite, and ilmenite are also present, in a microcrystalline or 

 crvptocrystalline groundmass. The rock is called a hornblende- 

 porphy rite. In certain varieties cordierite occurs, and is accounted 

 for by derivation from the adjacent shales. The reefs in the Silurian 

 and Ordovician rocks usually occur at or near the contact with 

 intrusive rocks. At Wood's Point the reefs are nearly horizontal, 

 traversing dykes and shales, the junction usually marking the 

 occurrence of rich ore. The author notes the ' almost invariable 

 association of gold in this class of deposit with rocks containing 

 original hornblende.' 



