PETROGRAPHICAL PROVINCE OF ESSEX COUNTY 289 



ophitic Dike 73, at Bemo's Ledge, Cape Ann, magnetite is want- 

 ing and the brown glass abundant. Flow structure is sometimes 

 seen. These varieties closelv resemble many normal olivine- 

 free basalts. 



Si0 2 

 Ti0 2 - 

 A1 2 3 - 

 Fe 2 3 

 FeO 

 MnO - 

 MgO 

 CaO - 

 Na 2 

 K 2 - 

 H 2 (no ) 

 H 2 (ignit.) 

 P,O s 



I 



47.12 



3- 2 7 

 14-43 



3-33 

 1 1. 71 



6.05 



9-63 

 2.58 

 1.1 1 

 0.28 

 o.34 



II 



48.75 

 °-99 



17.97 

 0.41 



13.62 

 0.91 



3-39 

 8.82 

 1.63 

 240 



0.60 

 0.68 



ill 



51.78 



1. 41 



12.79 



3-59 

 8.25 

 0.44 



7-63 

 10.70 



2.14 

 o.39 



0.63 

 0.14 



IV 



5I-36 



16.25 

 2.14 

 8.24 

 0.09 



7-97 

 10.27 



i-54 

 1 .06 



i-33 



v 

 36.85 



46 

 50 



60 



73 



99.85 100.17 99-89 100.28 91.14 



I. Diabase. Rockport. H. S. Washington anal. 

 II. Diabase. Medford, Mass. Sweetser anal. Traces of C0 2 and FeS 2 . 

 Probably A1 2 3 too high and MgO too low. Hobbs, Bull. Mus. Comp. Zool. XVI, 

 p. 9, 1888. 



III. Diabase. West Rock, New Haven, Conn. G. W. Hawes anal. Proc. U. S. 

 Nat. Mus., IV, p. 132, 1882. 



IV. Diabase. Watchung Mountain, Orange, N. J. L. G. Eakins anal. Bull. 

 148 U. S. Geol. Surv., p. 80, 1897. 



V. Diabase (?). Marblehead Neck. R. Pearce, Proc. Colo. Sci. Soc, IV, 

 1893. 



For purposes of analysis the freshest specimen was chosen 

 from a dike of ophitic diabase cutting the granite in the large 

 quarry pit at Rockport. It calls for little remark, except that 

 the alumina is rather low and the titanium oxide is high. It 

 resembles analyses of other diabases from Massachusetts, one of 

 which is given (II), but is more basic than the "traps" of Con- 

 necticut and New Jersey (III and IV). For purposes of com- 

 pleteness a partial analysis is given (V) of a so-called diabase 

 dike, briefly noticed by R. Pearce, from Marblehead Neck. It 

 is not very satisfactory. The silica is abnormally low, lime high, 



