Il8 THE JOURNAL OF GEOLOGY. 



feldspar particles. Within the feldspar, along the cracks, microperthite has 

 developed which does not show any dynamic action. The granite is much 

 later than the gneiss, but like it has to some extent suffered from dynamic 

 action. In general it is massive, or nearly so, but there are zones of shearing 

 where granulite and gneiss have developed. Also in one portion there is a 

 dark rock approaching a diorite, into which the granite grades, but this is 

 regarded as a basic segregation from the original magma. The crystalline 

 limestone is rather uniform in its character, but where intruded by the granite, 

 it is more coarsely crystalline, and various metamorphic minerals have devel- 

 oped. Near the base of the limestone is a pyroxenic rock which is schistose, 

 highly contorted, and is of somewhat doubtful origin, in the field being 

 regarded as sedimentary, and under the microscope having an appearance 

 which -suggests an igneous origin. In this pyroxenic gneiss occasionally 

 scapolite is found. The Potsdam is a pure vitreous quartzite, indurated by 

 the process of cementation. 



Nason,^ in 1893, describes the gneissic rocks bearing iron-ore in the 

 Adirondack region as precisely like the Mt. Hope type of rock, bearing the 

 New Jersey magnetites, and it is thought that the two are probably contem- 

 poraneous, bedded deposits. These gneissic ores are non-titaniferous, and are 

 to be discriminated from the titaniferous iron ores which are associated with 

 the labradorite rocks or norites of the region. These in occurrence and 

 association are wholly distinct from the ores belonging in the gneisses. 



Lawson^ describes the Santa Lucia granite of Carmelo Bay as resting 

 unconformably below the sedimentary rocks (Miocene) of the Carmelo series. 

 At the base of the latter is a fine basal conglomerate. Across the Bay of 

 Monterey, in the Santa Cruz range, granite without doubt of the same geol- 

 ogical range bears a similar relation to rocks which are of not later age than 

 Cretaceous. The granite is therefore, at the latest, of pre-Cretaceous age. 



C. R. Van Hise. 



' Notes on Some of the Iron-bearing Rocks of the Adirondack Mountains, by F. L. 

 Nason. Am. GeoL, Vol. XII., No. i, 1893, pp. 25-31- 



= The Geology of Carmelo Bay, by A. C. Lawson. Bull. Dept. GeoL, Univ. of 

 Cal., Berkeley, Vol. I., pp. 1-59. ' 



