166 
PBOCEEDINGS OF SOCIETIES. 
by substitution these equations become— 
P = W cot {u + 0), (7) 
P = W cot {u - 0). (8) 
As the rock mass in this case has been slightly pushed up the slope 
xy, we are to use equation (8) to find the horizontal force requisite to 
produce this reversed fault— 
P = 3-73 x W. 
It therefore required a horizontal force little less than four times the 
* weight of the rock mass to cause the reversed fault. 
If we wish to know the force requisite to prevent a direct fault, we 
must use equation (7)— 
P = 0*087 x W. 
If the horizontal force be less than about one-twelfth of the weight, 
and the line of fault already established, a direct fault or slip would 
occur. 
Such a force as this could never cause the overturning of the beds, 
or produce a reversed fault; and this latter kind of fault may occur 
whenever fractures of overturned oblique anticlinal and synclinal axes 
take place along the bend of the curves of strata. 
The Meeting then adjourned to the second Wednesday in May. 
GENERAL MEETING, MAY 12, 1858. 
The Peesident in the Chair. 
The Peesident exhibited, on the part of George M ‘Dowell, Esq., an 
ornament partly composed of aluminum. 
The President then read his paper on the occurrence of Gray Copper 
in the Yellow Sandstone near Boyle, county of Boscommon. The copper 
occurs in red slate, at a depth of about 2640 feet below the base of the 
Carboniferous Limestone. 
The President pointed out the analogy between this occurrence and 
that of copper in the south of Ireland, in similar beds, and that in each 
case the copper ore was either gray copper or blue copper, and never 
copper pyrites. 
Mr. J. Beete Jukes remarked on the singularity of the diffusion of 
copper in particular beds in the south-west of Ireland, and in the same 
beds in the north; and pointed out that light might possibly be thrown 
on the question of the deposit of ores in mineral veins by any one who 
would observe the relations between the ore in the beds and that in the 
lodes at Coosheen and elsewhere. 
The President then read his paper on the occurrence of some new 
and rare forms of Annellidoid tracks in the coal-measures of Lugacurren, 
Queen’s County. He illustrated his paper by rough drawings, separating 
them into two sets, of which he believed one to be a molluscan track, 
