1855.] FORBES FOLIATION OF ROCKS. 175 



have observed that the same phsenomena have been caused by the 

 appearance of totally different chemical compounds. 



(Case 12.) — At Pusaasen, a little north of east of the locality de- 

 scribed above, and illustrated by fig. 4, p. 172, we have a bed of lime- 

 stone, apparently either the same, or one parallel to it, which lies on 

 gneiss, and appears to run in the same direction as the former. 

 Here I found that several feet of the lower part of this bed were 

 foliated by the introduction of the mineral termed chondrodite (a 

 fluosilicate of magnesia), which was arranged perfectly parallel to the 

 micaceous foliation of the gneiss, as well as of that of the limestone. 

 It may be also mentioned that the chondrodite here is associated 

 with the black spinel, precisely as at Sparta in the United States. 



I have also observed in Norway many cases of foliation where this 

 structure has been induced by the presence of small laminae or folia 

 of oxide of iron, sometimes to the almost total exclusion of other 

 foliating minerals. I have found this to be the case, on the small 

 scale, in Nissedal, at Langoe, and at Dybsund Holm, near Krageroe. 

 On a larger scale, it appeared at Ronningen, in Drangedal, where the 

 gneiss was often very strongly foliated by scales of oxide of iron, and 

 having a very characteristic red appearance. This foliation appeared 

 not to disturb in any way that of the adjoining gneiss. 



The foliation of rocks by means of oxide of iron is not peculiar, 

 however, to Norway, From observations recently communicated to 

 me by Lieut. Aytoun, Bengal Artillery, this is often the case in 

 Hindostan. He states that at one of the small outliers of the Kup- 

 put-good range of mountains a very fine example of this may be 

 seen. The rock is a siliceous talcy schist, and strikes N.N.W., 

 dipping 50° E. ; the beds thus foliated are from 60 to 80 feet thick, 

 and extend for several miles. In some hand-specimens received from 

 Mr. Aytoun there are portions of the talcy schist having the talc 

 entirely replaced by scales of black magnetic oxide of iron, which 

 also shows itself particularly well developed along the joints. 



In the valley of the Mulpurba, about eight miles south of Belgaum, 

 in the Deccan, Mr. Aytoun has observed many instances of mica- 

 schist and clay-slate running 5° N.W., and dipping 80° E., in which 

 small bands, from ^ to ^ inch thick, were foliated by oxide of iron, 

 and many hand-specimens of which possessed a distinct polarity. 



It is often the case in Norway that some strata or parts of strata, 

 extending often for miles, present a peculiar foliated arrangement, 

 due to the introduction or appearance of certain metallic compounds 

 and the greater or less exclusion of the usual foliating silicates. Thus 

 at Kongsberg, near Tvedestrand, in Drangedal, in Espedalen, and 

 several other places I have found various sulphurets showing them- 

 selves ; and at Modum and Snarum, also at Vena, near Askersund in 

 Sweden, arseniurets show themselves under similar circumstances. 



The details connected with these occurrences are particularly 

 interesting, and important also in an economical point of view ; but 

 they cannot be brought within the limits of this communication : I 

 trust, however, at a future period to bring some observations on the 

 subject before the Society. 



