138 The American Geologist. March, i89o 
wide are holocryslalline, and another, forty feet, is porphyritic 
some other structural factor must have entered. In the por- 
phyrites, the olivine, when present, is the most striking min- 
eral. Its size, even in the very narrow glassy examples, is 
hardly les than in the large dikes. Its crystallization must 
have occurred at a relatively early period, — and itself was well 
developed while all the others except magnetite were still un- 
differentiated in the magma. 
On account of lack of opportunities and time, the chemical 
examination of these dikes has not kept pace with the micro- 
scopic, much to the writer's regret. One analysis of the large 
augite-prophyrite (No. 92.) has been kindly made by Mr. H. 
A. Flint in the laboratories of the University, and is here ap-, 
pended : 
Loss on ignition 0.69 0.68 
Si 02 51.93 51.72 
Al2 03 18.13? o-Tp. 
Fe2 03 8.92i" ^'-^^ 
CaO 9.82 9.95 
Mg O 5.30 5.31 
Na2 O 4.34 4.35 
K2 1.42 1.46 
It would appear from this that the feldspar is probably an 
oligoclase. The rock is certainly more acidic than the general 
run of the dikes. 
The writer was much assisted while in the field by Mr. Har- 
ris Kennedy, of Roxbury, Mass., and after he had been com- 
pelled to leave the region, Mr. Kennedy continued the work in 
some neighboring localities. The dikes are found on cape 
Porpoise, two miles north of the limits of the map, and at the 
mouth of York river, eight or ten miles south of Bald Cliff. 
The olivine-diabase at Lewiston, inland and to the north, the 
so-called black granite (determined to be olivine-diabase by 
G. P. Merrill, — 10th Census, Rep't on Building Stones, p. 24) 
at Addison point, away along the eastern coast, and the peri- 
dotite at Little Deer Isle, (G. P. Merrill, Amer. Jour. June, 
1888.) are other allied rocks which have already been noted in 
the state. 
It appears that the commonest type of dike rock elsewhere 
noted, is an olivine diabase, or simply a diabase without oli- 
vine. Haworth' found such in the Archaean of Missouri ; 
Hobbs,^ the same in Massachusetts ; Lawson,-^ in the Prov- 
inces north of Minnesota ; Herrick" and others, at Michii:)ico- 
