456 STRATIGRAPHICAL GEOLOGY. 



down in previous chapters regarding the great antiquity of most of the 

 New Hampshire rocks. 



12. In case the Coos schists are to be regarded as of Helderberg age, 

 the whole of the Calciferous mica schist must be taken with them. These 

 occupy about a third of the area of Vermont, and such reference would 

 add much to the breadth of Paleozoic areas in New England. This was 

 very nearly the view of Logan, of twenty years since, who supposed that 

 this formation belonged to the Niagara group. 



13. There is no connection whatever between the Coos and Montalban 

 groups, as is inferred by Prof. Dana. If we grant the former to be Hel- 

 derberg, it does not bring the latter any higher up, since all the White 

 Mountain rocks have been shown to underlie them unconformably. 



14. There is no interstratification of the chloritic rocks at Littleton 

 with the Helderberg. There may be a few small bunches of chlorite in 

 the limestone. Chlorite is a mineral that may exist wherever rocks have 

 been elevated and permeated by fluids transporting the proper chemical 

 reagents. Its presence does not indicate a high degree of metamorphism. 

 The chloritic rocks do not come anywhere near the Bernardston series, 

 so that it is clear they do not belong to the Helderberg series, even upon 

 the most comprehensive definition of them. 



15. It is probable that the epoch of elevation of the Helderberg rocks 

 along the Connecticut valley occurred in middle Devonian times. We 

 find at Mcmphremagog lake the upper Helderberg limestone, and also 

 elsewhere in northern New England, but no later groups. In the east 

 part of Maine I have found Helderberg strata, elevated at a considerable 

 angle, overlaid unconformably by Hamilton beds. It is presumable that 

 this epoch of elevation in Maine may correspond with that in this valley. 

 I am persuaded it was an epoch of elevation of the greatest importance, 

 perhaps more so than any other that has manifested itself in New Eng- 

 land. (See page 263.) 



16. Interpreting the facts as above to harmonize with what seems well 

 established about the older New Hampshire rocks, it is clear that we may 

 still eliminate the thoroughly crystalline schists from the catalogue of 

 Paleozoic formations ; and, conversely, the Helderberg rocks have not 

 been very much metamorphosed, even if we refer the Coiis rocks to that 

 age. Staurolite and andalusite may be found anywhere, because their 



