JPirsson and Washington — Geology of Bed Hill, N. H. 269 



The feldspars are entirely of alkalic character, no soda-lime 

 varieties having been observed. They consist of orthoclase and 

 albite which unite in forming microperthite and cryptoperthite 

 intergrowths, both of which are found together and often 

 indeed in the same individual. The albite lamellae have as 

 usual the vertical axis and the face 010 in common with the 

 orthoclase; in many cases where they are of large size they 

 show twinning according to the albite law. In a section per- 

 pendicular to the bisectrix c and approximately parallel to 010 

 the albite lamellae form elongated lenticular bodies of irreg- 

 ular shape and often anastamosing; their elongation is in the- 

 general direction of the vertical axis. When this section is 

 observed with a low power there is a general appearance of 

 uniformity, though it has a wavy moire aspect, and it extin- 

 guishes at 11° from the trace of the basal cleavage 001 in the 

 obtuse angle /3. When studied with a high power the lamellae, 

 spoken of above, appear ; they form a very large proportion, 

 perhaps one half of the host, their birefringence is higher and 

 they extinguish at about 16° from the cleavage; this latter 

 shows they are albite or perhaps albite with a little of the 

 anorthite molecule present. The host extinguishes at 6°, 

 which shows it to be orthoclase. It is to be noted that 11° is 

 the mean between 6° and 16°. It is noticed in the study of 

 these mixed feldspars that the cleavage parallel to 010 is often 

 well developed in the section while that of 001 is compar- 

 atively rare, and it is suggested that this may be due to the 

 fact that they possess the face (and cleavage) 010 in common 

 while the basal cleavage is not a uniform direction through 

 the interpenetrating masses. While the feldspars are usually 

 free from inclusions, in some cases they were noticed to contain 

 slender microlites of eegirite. In the type material they are 

 quite fresh, in other places somewhat kaolinized. 



The nephelite presents no unusual features : it is in some 

 places altered in part to a micaceous, scaly mineral, in others 

 weathered to dull earthly kaolin; in most of the specimens of 

 fresh rock it is fresh and clear, only in places it is bordered, 

 edged or so associated with cancrinite as to suggest the latter 

 as a secondary mineral. Much of the nephelite tends to rough 

 crystal form of the common thick tabular habit. 



The sodalite is much like the nephelite in preservation, gen- 

 erally fresh, and often the last to crystallize, filling angular 

 interstices. The S0 3 of the analysis shows that the nosean 

 molecule must also be present in small amount. In the hand- 

 specimen the sodalite is white to gray, sometimes with a green- 

 ish, sometimes pinkish tinge ; the characteristic bright blue it 

 shows in many rocks and which is mentioned by Bayley (loc. 

 cit.), has nowhere been found, in the rock mass by the writer. 



