726 THE JOURNAL OF GEOLOGY. 



found Ordovician fossils in the limestone belts some distance to 

 the north and Cambrian fossils at Stissing Mountain to the south- 

 west. 



Lithological Character of Horizons. — (a) Ca?iaan Dolomite. This 

 bed seems to be very rich in magnesia, the rock being in some 

 cases at least a true dolomite. This is shown by a number of 

 analyses of it by Mr. J. S. Adam. 1 This rock appears at the sur- 

 face only in the extreme southeastern portion of the area here 

 considered, where it presents few features different from those 

 which are common to the Egremont Limestone. Farther to the 

 eastward, however, and particularly in the vicinity of Canaan, it 

 is often characterized by the presence of interesting metamorphic 

 minerals, the well known salite and tremolite of that locality. 

 Phlogopite also has in one or two instances been found. In its 

 upper layers, where it approaches the overlying Riga Schist, the 

 rock may become graphitic, as at Ore Hill. As it appears in the 

 vicinity of the mountain, however, the rock presents no charac- 

 ters which can be relied upon to distinguish it from the higher 

 Egremont Limestone, and the differentiation is based on strati- 

 graphy alone. 



(&) Riga Schist. — This horizon is tolerably uniform in charac- 

 ter, the principal differences being in the presence and variable 

 size of the metamorphic mineral individuals. Strictly speaking 

 the rock is a gneiss, owing to the abundance of feldspar, but in 

 order to distinguish it from more feldspathic and more or less 

 granitoid gneisses lying east of the Housatonic River, it is best 

 to refer to it as a schist, which it most resembles in structure. It 

 almost invariably is porphyritic from the presence of lenticular 

 to spherical grains of an acid plagioclase. The base is usually 

 composed of feldspar, quartz, and a colorless mica (in part seri- 

 cite) and biotite. Considerable graphite often exists in this base 

 as does also ilmenite. Chlorite when present is usually in small 

 amount. Garnets, staurolite, ottrelite, and biotite, as well as 

 plagioclase, are developed at many localities. On the summit 

 of the Lion's Head the rock contains garnets (rhombic dodeca- 



1 See Am. Jour. Sci., vol. xlv. p. 404, foot note. 



