432 Scientific Intelligence. 
such cases the two planes vary in strike Lye ty The cleavage has a 
northerly dip at angles varying from 25° to 65° 
the Barmouth chain the strike of 3 i wa is somewhat irreg- 
ular; but its mean direction is north and south, and its dip is from east 
60° to west 60°. 
In the district intersected by the great porphyritic eruption of Arenig, 
Arran Mowddy, &c., the planes of cleavage have lost their original 
bearings, and ape subject to pi eres irregularit both in respect to 
direction and dip; and the observation applies to the district . 
ower Silurian rocks extending along the Holyhead road betwee 
Bryn-y-ddinas and Cor 
rom the ecuenasians: that the aye ee of the planes of cleavage 
depends, not on the varying position the beds at each particular 
spot, but on their main position, the hot a infers that slaty cleavage 
cannot have arisen from any power analogous to that of crystalliza- 
tion; and from the almost mathematical regularity with which those 
planes are arranged, he concludes that they are not the effect of me- 
nin force or pressure exerted at the moving or upheaving of the 
"The author further concludes from his observations, that in those 
of bedding and cleavage meet at an angle of from 15° to 30°; and 
hence he infers, that in those cases where, at the time of cleavage, the 
beds were horizontal, such was also the angle at which the cleavage 
intersected the bedding (15° to 30°). The author further observed, - 
that in the quarries of North Waies which afford the slate of the best 
quality, the bedding and cleavage rarely meet at an angle less than 25°, 
and never less than 20°; and that whenever the angle is less than 20°, 
the slate is of inferior ronan An increase in the angle at which the 
planes meet has no injurious effect; for in many instances when the 
vars is of the best quality, the sh of intersection is 45° ons. sh 
war 
9. On the Salt and Salt Lakes of Algeria ; by H. Fours (Ann. 
des Mines, 1846, ix, 541. )—The extended memoir of M. Fournel gives 
many piece details and important sedonienn, with seach = | 
salt deposits of Algeria. Salt lakes or marshes and streams appear to 
be innumerable; and besides these, banks and even mountains of salt 
are met with. The salt is associated with gypsum. The most impors 
imbedded in the cretaceous a The mines five leagues west 
The salt is coutke white and pure, and of good wales and the qua 
tity not less than 127 millions of cubic meters. There is a moun iain 
of salt near this lake. Lake ef Mélah, in the province of Oran, is a0- 
other of the same kind, but less extensive. 
10. Volcanic Peak of the Island of Fogo, Cape Verds; by C. 
Devitte, (Bull. Soc. Geol. de France, 1846, 2d ser., iii, 656.)—The 
