LITHOLOGY. 199 



sections plenty of both hornblende and biotite are found between the 

 larger grahis of quartz and feldspar. The hornblende is very deeply 

 colored, and the light that passes in one direction is green. Consider- 

 able magnetite and apatite and some oligoclase are present. A specimen 

 from Iron mountain in Bartlett only differs in that the biotite and horn- 

 blende, being more abundant, are more conspicuous in the hand speci- 

 mens; and the orthoclase possesses at times a pretty and striking opal- 

 escence, which is due to minute cleavages, as has already been explained. 

 Very wide variations take place in the proportion in which the acces- 

 sory ingredients are present, while the rock maintains unmodified its 

 typical color and appearance. For example : biotite and hornblende 

 are sometimes very conspicuous ; but, again, as on Mt. Lafayette, these 

 ingredients are very sparingly present, and macroscopically are scarcely 

 recognizable, and the rock differs, therefore, but little from granitell. At 

 Ossipee and at Frankenstein cliff the biotite is almost absent, while horn- 

 blende is prominent, and the rock becomes a hornblende granite. At 

 Stark the quartz and biotite are both withdrawn, and the rock becomes 

 sienite. These rocks, at all the localities mentioned, are regarded by 

 Prof. Hitchcock as eruptive. From their peculiar appearance they have 

 attracted considerable attention, and some doubts have been entertained 

 in regard to their classification; but with the exception of the Stark 

 variety they are simply granites, with unessential variations in the rela- 

 tive amounts of the accessories, and their only peculiarity is the con- 

 stancy in the character of the feldspar, which in all is the preponderating 

 mineral. The clearness and purity of this feldspar, which in thin sec- 

 tions is in marked contrast to that of the disintegrating granites, such as 

 as those in Conway, indicate that these granites will remain firm and 

 solid after time has worn away the Conway rocks. 



Some granites occur in Albany, which have certain characteristics 

 which extend over a class to which the name Albany granite has been 

 given. They are very hard and durable rocks, and possess some of the 

 peculiarities of the granites last described. The characteristic features 

 of these granites are, that they are composed of a mass of minute crys- 

 tals in which larger crystals of orthoclase are often porphyritically devel- 

 oped ; and the black constituents, like little specks, are so scattered 

 through the ground mass as to give rise to an appearance which has 



