Wadsworth.] 224 [May 16, 



6. Argillite quarry near the Cambridge Alms House, — "green- 

 stone " and " trap." 



7. Elm Street, northwest side, an argillite quarry with three 

 dikes of " trap," one of " greenstone " and one of " porphyry." The 

 trap shows in the westerly dike the usual prismatic jointing. The 

 middle trap dike faults the " porphyry," the opposite parts being lat- 

 erally separated by about six feet. The same dike also cuts the 

 greenstone, showing that it is of more recent date than either the 

 "porphyry" or "greenstone." The easterly dike extends on both 

 sides of Elm St., and is porphyritic by reason of crystals of clino- 

 clase and some calcite. Several layers of sandstone are found in this 

 quarry as well as in others in the argillite which closely resemble that 

 found in connection with the conglomerate at Brighton. The 

 -" porphyry " in its passage through the slate and sandstone, takes 

 ■various directions, horizontal, perpendicular and oblique, inclined to 

 the north. 



8. On Chandler St., near the last mentioned quarry, there are 

 three " trap " dikes and one of " greenstone." 



9. Between Elm and Willow Streets, also on both sides of Wil- 

 low St., and on Appleton St., the " greenstone " outcrops in several 

 places; and the " trap" is to be seen on the west end of Appleton 

 St. and the east side of Willow St. 



10. Near the old " Powder House," corner of Elm St. and Broad- 

 way, — " diorite." 



11. Fremont St., — "greenstone " and " porphyry." This is the 

 best location of the latter, which is here almost interstratified with 

 the argillite, but shows its intrusive character by its shoulders and 

 branches, also by its breaking across the stratification in some places. 



12. In that part of Somerville included between Mystic Avenue, 

 Temple, Bond, Heath and Brooks Streets, numerous quarries exist, 

 and very many outcrops of " trap " and " greenstone " occur. 



13. Between Bond and Heath Streets, — " trap." 



14. Near the centre of Vernon St., — " porphyry," or a decompos 

 ing " greenstone." 



.15. Adams' Ledge on School St., opposite Howe St., — "trap" 

 and "greenstone." 



16. Corner of Marshall and Pearl Streets, — "greenstone." 



17. West corner of Walnut and Pearl Streets- 

 on the east corner — " trap." 



; 



