148 PROCEEDINGS MANCHESTER INSTITUTE 



Of feldspar, very fine specimens of orthoclase, the flesh red, 

 are abundant at the city ledge near the poor farm. I have se- 

 cured some fine crystals, though not abundantly. This ortho- 

 clase is rich in potash. Dana gives in his analysis 16.9 parts in 

 the 100. It appears to me that if pulverized it might be a valu- 

 able fertilizer and a great benefit to our worn-out lands. The 

 varieties of feldspar are so numerous in this vicinity that it is 

 needless- to particularize localities. . 



I will call attention also to the numerous detached boulders of 

 porphyritic gneiss that may be observed existing in great abund- 

 ance all over this locality. They are erratic rocks that have been 

 brought here from the vicinity of Winnipesauke and Sunapee 

 lakes, where the rock occurs in the vast ledges of those localities. 

 They were transported here in the ice drift of the great glacial 

 age, many of them retaining the polished or streaked appearance 

 which they received in their transit. You will readily recognize 

 them. In form they are usually rounded, the color of the rock 

 mass being usually greyish, sometimes black. Interspersed in the 

 mass you will find numerous crystals of a white or lightish feld- 

 spar. These crystals measure from a quarter to two or three 

 inches in length. The gneissoid rocks are very abundant in all 

 sections of the city, particularly in the neighborhood of the Man- 

 ter brook, south of the city reservoir, where the rock is of a pink- 

 ish or flesh color and impregnated with streaks of biotite. Most 

 of the rock formations around Massabesic pond are of gneiss. 

 This rock belongs to the class of granites, but is distinguished in 

 having the mica deposited in streaks or veins instead in a homo- 

 genous mass, like true granite. 



I must not overlook the crystals of magnetite, a form of iron, 

 occasionally found in the old wall stones in this . vicinity, notably 

 in the neighborhood of the city farm. I judge that they also 

 came in the ice drift from the north, from the fact that I have 

 not observed them in the bed rocks about here. Near the junc- 

 tion of Milton and Merrimack streets may be observed, opposite 

 A. H. Paige's hbuse, and directly in the street, the cropping out 

 of a granite ledge with an extensive seam of (amphibolyte) horn 

 blende of the variety Actinolyte having slender light green crys- 

 ■ tals. It is in massive form and easily accessible with proper tools. 



