129 



is, of course, valueless as a test of age, when applied to widely 

 separated rocks ; but within the same limited region such in- 

 dications should, I think, be allowed some weight, in the 

 absence of better criteria. 



All the Montalban rocks in Massachusetts, west of the 

 Nashua Valley, have approximately N.— S. strikes. East of 

 the Nashua River, and north of Worcester, however, the line 

 of strike gradually shifts toward N.E. ; and between the eastern 

 rim of this valley and the eastern border of the formation the 

 beds of this series conform closely in strike with the stratified 

 rocks of the Huronian system. South of Worcester, along the 

 valley of the Blackstone River and east of the same to the 

 limits of the formation, the strike is at right angles to that just 

 noted, or N.W.-S.E. This continues through the north-east 

 corner of Rhode Island, gradually approximating more nearly 

 to E.-W. ; and beyond the Carboniferous formation and Nar- 

 ragansett Bay the Montalban strata reappear and extend 

 through southern Bristol and Plymouth Counties with an E.- 

 W. strike, varying toward the north, and again exhibiting a 

 tendency to parallelism with the fundamental structure lines of 

 the Huronian system. 1 



The principal lithological constituents of the Montalban 

 series in Eastern Massachusetts are : — 



1. Granite, 



2. Gneiss, 



3. Mica Slate, 



4. Argillite, 



5. Limestone. 



As in the Huronian system, these groups or divisions are 

 believed to have chronologic as well as lithologic value ; and 

 their order of sequence, with the exception perhaps of the 

 limestone, is as stated above. Prof. Hitchcock, in his final re- 



1 These various lines of strike, as well as other points of interest in the geognosy of 

 the State, are well shown on the map prepared for that purpose by Prof. Edward 

 Hitchcock, and contained in his Final Report on the Geology of Massachusetts. 



OCCAS. PAPERS B. S. N. H. — III. 9 



