1'28 NEW YORK STATE MUSEUM 



from the Northumberland rock that there can be no question 

 of correlating them. 



The Triassic traps are uniformly diabases. They are in 

 general quite similar to the Northumberland rock except that 

 olivin is usually lacking in them. But Professor Emerson, while 

 remarking on the absence of olivin in the main trap sheets of the 

 Massachusetts Trias, reports it as more or less abundant in the 

 smaller dikes which cut the adjacent gneisses, and in some of 

 the later plugs. 1 It is also sometimes present in the New York 

 and New Jersey traps. Therefore the presence of olivin, while 

 enforcing caution as to the reference of the Northumberland 

 rock to the Trias, is not an insuperable objection. 



The writer is therefore disposed to refer the Northumberland 

 rock to the Trias, because of its character, but it should be em- 

 phasized that it is a disposition simply. It is put forward as a 

 working hypothesis. The first sight of the thin sections sug- 

 gested the reference, and it is of interest to note that Professor 

 Wood worth had come to the same conclusion on wholly different 

 grounds. An obvious objection to the reference at once arises, 

 its isolation and distance from any known Trias traps and sedi- 

 ments. In answer to this it may be legitimately argued that 

 the remnants of the Trias formation can give no idea of its 

 original extent, and that the traps might well therefore have a 

 much wider distribution at present than the sediments, since 

 they came up from beneath. Also that there seems no a priori 

 reason why they may not have had an original wider distribu- 

 tion than the sediments, since the disturbances which character- 

 ized the period can hardly have been confined to the actual 

 troughs where deposition was going on, or, rather, where exten- 

 sive deposition was going on. To quote from a letter of Pro- 

 fessor Woodworth's : 2 



I have thought from the habit and mode of occurrence of this 

 rock, that it may be a part of the Triassic eruptions lying on, or 



1 V. S. Geol. Sur. Monograph. 29:412,493. 



a Professor Woodworth and I arrived at the opinion of the Triassic age 

 of the Northumberland rock independently, from different lines of evidence 

 and prior to entering into correspondence on the matter. 



