292 Canadian Record of Science. 



alternating with the gneiss. Their width varies from one 

 to several hundred yards, and their length from one-half 

 to eight English miles. Some of the larger bands are 

 represented on the accompanying map. The character of 

 the anorthosite varies somewhat in the different bands, 

 but on the whole it resembles that of the Morin area. In 

 general these bands are sharply defined against the gneiss, 

 with the exception of that near St. Jerome, where the 

 surrounding anorthosite appears to gradually pass into 

 the gneiss. As distinguished from that of the main mass, 

 the anorthosite of these bands often contains more or less 

 hornblende, biotite and garnet. In one place scapolite 

 also appears in considerable quantity, probably as a pro- 

 duct of the alteration of plagioclase, as in the case of the 

 well known spotted gabbros of Norway. These anorthosite 

 bands, moreover, present a more or less distinct arrange- 

 ment of the constituents in the direction of their long axis. 

 Under the microscope the above described granulation 

 of the constituents is seen excellently developed. Together 

 with these anorthosite bands which have the character 

 and the appearance of eruptive rocks, we find in many 

 places in the Laurentian gneiss, particularly on the east 

 side of the Morin mass, interstratified layers of a dark 

 pyroxene gneiss which gradually passes into the ordinary 

 gneisses. These have quite a different appearance from 

 anorthosite, being much richer in coloured constituents. 

 They contain augite, hypersthene and plagioclase in quan- 

 tity, very often biotite, hornblende, a little quartz, and 

 considerable quantities of an untwinned feldspar which 

 probably consists mostly of orthoclase. We also meet 

 these so-called "basic gneisses" in many other widely 

 separated districts of the Laurentian, but neither these 

 nor the anorthosite bands have been as yet thoroughly 

 examined from a mineralogical standpoint. In a report 

 on the district to be published before long by the Geolo- 

 gical Survey of Canada they will be more fully discussed. 



