CLASSIFICATION OF THE NEW HAMPSHIRE FORMATIONS. 6/1 



ing need be said of the two Helderberg series, as their relations are well 

 known. There are no formations in the state of later date than the 

 Lower Helderberg, save the surface deposits. Full details respecting 

 them may be expected in Part III. 



Thickness of the Formations. 



Making all suitable allowances for repetition of strata by flexures, I 

 venture to add a column indicative of the thickness of our New Hamp- 

 shire formations. For future reference, I will briefly state the localities 

 relied upon for these estimates. 



The figures for the surface deposits are taken from a general impression 

 of the viaxinia. The thickness of the North Lisbon Helderberg has been 

 roughly estimated at 500 feet (p. 338). In the Vermont report (vol. i, p, 

 449) the thickness of the Coventry Upper Helderberg deposit is esti- 

 mated at more than 200 feet. The Calciferous mica schist, at its min- 

 imum, perhaps, is given in the same report (vol. ii, p. 617) as 4,800 feet. 

 I have used the thickness of 3,000 for staurolite slate and 3,300 for the 

 mica schist of the Coos group, from the measurements taken from the 

 section in Fig. 28. On the Orford section the same are respectively 

 2,700 and 2,700 feet. 



On the Lyme section they are 2,250 feet (reduced one half from the old 

 measurement in the annual report, to allow the further folding indicated 

 in Fig 54) and 1,500. The green schists following, 3,791 feet, may pos- 

 sibly be the equivalents of the Calciferous mica schist. In Hanover the 

 slates amount to 2,400 feet and the schists to 2,100. These various 

 measurements indicate that the thickness is not constant. The quartzite 

 in Hanover is 800 feet, and in Orford 1,000 feet thick. I will use double 

 the thickness stated in conection with Fig. 28 for the clay slates (Cam- 

 brian), because the inversion supposed to be present is doubtful, and 3,000 

 feet will better express our notion of the usual thickness of this formation. 



In Andover the thickness of the Kearsarge group (Fig. 103), allowing 

 five foldings, would be 1,300 feet. The Rockingham group cannot be 

 measured satisfactorily. The average of two attempts (Figs. 99, 100) 

 gives us 6,000 feet. For the Merrimack group, the thickness of one side 

 of the Epping synclinal (Fig. 106) is taken for the standard. 



The thickness of the Huronian members is taken from Fig. 28, except 



