6/2 STRATIGRAPHICAL GEOLOGY, 



the hornblende group. We assume fifteen sixteenths of a mile as its 

 breadth, and 40° as the average dip o£ this band in Hanover. Dividing 

 the result by two, the quotient is 1,580. 



For the Montalban series, I will figure only upon the fibrolite and the 

 ordinary series. The first, three tenths of a mile wide, at an angle of 60°, 

 will show 1,370 feet thickness. Perhaps a fair average of the Montalban 

 series may be obtained from a section between Glen Ellis falls and the 

 north base of Mt. Pequawket, allowing for two folds and an average dip 

 of 50°. This is not satisfactory, but the result of the calculation, approx- 

 imately 10,000 feet, expresses fairly our idea of the thickness of the series. 



For the thickness of the Lake series I have calculated the breadth of 

 one half the Manchester range, or from Hallsville to near the south-east 

 corner of the township, three and three fourths miles, at an average dip 

 of 70°, making 18,600 feet. The breadth of the Bethlehem series in 

 Hanover is calculated to be about 6,300 feet. The upper division may 

 be estimated as 5,000 feet. Taking the broadest part of the porphyritic 

 gneiss from Washington to Warner (Fig. 85), and allowing for seven 

 flexures, we shall get 5,000 feet thickness for it. 



Geological Map. 



Constant allusion has been made to the general geological map of the 

 state in the descriptions of the rocks. This has been drawn upon the 

 scale of two and a half miles to the inch, and contours for every one 

 hundred feet of altitude. It embraces portions of Maine, Vermont, and 

 Quebec, and is engraved upon six sheets. The facts embodied upon it, 

 both topographical and geological, have been derived from our survey. 

 The formations represented are essentially those of the stratigraphical 

 column given on a subsequent page, with such variations as the state of 

 the case or the degree of knowledge allows. Many persons will recog- 

 nize in it the features of a topographical atlas of the state recently pub- 

 lished by Comstock & Kline. These gentlemen were allowed to use our 

 delineation for their map. Quite a number of improvements in detail 

 over this subscription map will be found upon it by those who examine 

 the topography critically, and it covers a larger area. Many geological 

 facts are added, besides the difference in paper and the elegant coloring. 

 In case the distribution of the formations differs from the description of 



