Vol. 69.] METAMORPHOSED SEDIMENTS IK BRITISH EASI AERICA. 535 



cut, and have accordingly had to rely on examples collected from 

 the immediate vicinity. 



(4) A calc-mica rock containing lenticles of biotite-gneiss, 

 and 3 feet 8 inches thick. At first sight, the junction between 

 Beds 3 and 4 appears to be sharply defined enough, but with a 

 little care the two rocks can be seen to pass one into the other 

 by the incoming of calcite-crystals in the underlying biotite-gneiss, 

 segregated, moreover, into laminse. These crystals, when thus 

 gathered into streaks, are associated with hornblende, and form 

 a passage-zone some 4 or 5 inches thick. A foot or so away, 

 where the line of junction is more cleaiiy defined, a lenticle of 

 biotite-gneiss, about 3 inches long, is separated from the main 

 bed of the underlying rock by a thin band of calcite crystals ; 

 while, higher up in the calc-rock, lenticles of the same type, an 

 inch and a half thick, themselves containing thin streaks of calcite- 

 crystals, are not uncommon. In addition to this, lenticles com- 

 posed principally of hornblende, and about 10 inches long by half 

 an inch thick, may be observed. 



The remainder of the section calls for less comment. 



(5) Hornblende-schist. A rock similar to No. 1. Thickness 

 = 1 foot. 



(6) Impure calc-rock, 2 feet, containing quartz-felspar 

 strings, having a direction parallel to the trend of the foliation, and, 

 so far as could be observed, unconnected with any dyke-rock. 



(7) Coarse quartz-felspar vein. Thickness =2 feet. 



(8) Hornblende-schist. Thickness = 2 feet. 



(9) Impure calc-rock resembling No. 5, and about 4 feet 

 thick, the top not being clearly seen. 



From the foregoing facts I conclude that we have here a section 

 of metamorphosed sediments, varying from an arenaceous to a 

 calcareous type, and that a passage-zone between a calc-mica-rock 

 and a biotite-gneiss does actually exist. 



The relationship between a thin layer of the hornblende-schist 

 and the common type of impure marble is shown in a specimen 

 collected a few yards farther up the valley. A thin section shows 

 on the one hand a hornblende-schist, with rare malacolite, on the 

 other a coarse marble. The intermediate zone, 4 to 5 mm. wide, 

 contains hornblende after malacolite, as also calcite and sphene, 

 the latter in noticeable quantity, although both are greatly sub- 

 ordinate to the other two first-named minerals. In addition there 

 is some water-clear plagioclase having small extinction-angles. 

 Another instance of a similar association of hornblende-schist 

 and marble was found in the same stream-bed, where a lamina 

 1 inch thick divides two calc-rocks. The former is a hornblende- 

 schist, the hornblende being usually idiomorphic to the extent of 

 showing prismatic and clinopinacoid faces, although the latter are 

 often absent. Microcline and plagioclase, with low extinction- 

 angles, are common, and there is much untwinned felspar and 

 quartz. In regard to accessory minerals, sphene, zircon, and apatite 



2n2 



