ERRONEOUS DETERMINATION BY HAWES. 245 



Smith, who has kindly furnished to the writer all the material desired. 

 In a letter accompanying the specimens Mr. Smith says : 



"The rock I obtained on the northeastern side of Keel hill, on land belonging t<> 

 Mr. \Y. II. Mason. The ledge lie.- in the pasture mi the southwestern side <>f the 

 road." 



In this variety the structure is more nearly granular than in the 

 case of either of the others, and the rock is much fresher. The large 

 twinned feldspars that are so characteristic of the first two varieties de- 

 scribed are lacking in this. The groundmass of the hand-specimen is of 

 a grayish-white color and is composed of brilliantly glistening facets of 

 an lintwinned feldspar and small dull gray areas of eleolite. Occasion- 

 ally tiny Carlsbad twins of orthoclase may lie detected, but these are rare. 

 In this groundmass are Large columnar crystals of a feldspar like that of 

 the smaller grains, and large black grains of hornblende, frequently with 

 idiomorphic outlines. The resemblance of this rock to a typical horn- 

 blende-syenite is so close that there need lie no surprise that it was called 

 such by so careful an observer as Hawes. The eleolite is not recognizable 

 in the hand-specimen until after its presence has been ascertained by 

 microscopical and chemical tests. 



Microscopic Description and Discussion of Chemical Analyses. — A single 

 glance at its thin sections shows the Red hill rock to he quite different 

 in structure as well as in composition from the Maine eleolite-syenite. 

 Its components are a light-colored augite, bright green ami dark brownish- 

 green hornblende, brown biotite, feldspar, eleolite and sodalite as essen- 

 tials, and magnetite, sphene, apatite and Leucoxene as accessories. The 

 oldest of these are magnetite, apatite and sphene. The former is in little 

 irregular grains and accumulations of grains, and the sphene is in rounded 

 and irregular masses and in double wedge-shaped crystals, with the usual 

 color and pleochroism of this mineral. The apatite is present in the 

 familiar colorless prisms so well known. All occur as inclusions in all 

 the other constituents, hut they are more frequently in and around the 

 aggregates of the bisilicates than elsewhere. 



Ne\t in age follow the iron c pounds. These, as has been stated, are 



augite, hornblende and biotite, which, together with apatite, magnetite 

 and leucoxene, form aggregates or accumulations, the primary constitu- 

 ents of which separated from the magma some time before the elements 

 of the Light-colored groundmass in which they are imbedded. 



But little of the augite remains in the rock. That which is presenl 

 exists as very liglil green, almost colorless core-, whose peripheries are 

 fringed with bright green hornblende. The maximum extinction observed 

 in these cores is 37°. In all cases the augite lie- imbedded In an irregular 

 aggregate of the green hornblende, biotite and leucoxene, -of which the 



