Sections and Map of the Strata. 



523 



Sections and Map of the Direction of the Strata, accompanying this 



Report. 



In order to give as correct a view as I am able of the course of our 

 inclined strata and their dip, I have given Plate XVI to illustrate th.3 

 former, and Plate XVII and XVIII, to exhibit the latter. For on 

 these two circumstances the whole argument for proving the elevation 

 of the different systems of strata at different epoch, rests. 



The instruments which I have employed for ascertaining the di- 

 rection and dip of the strata, area good pocket compass and a clinom- 

 eter. I confess, however, that in consequence of the very common 

 oscillation of the dip and direction within short distances, I have been 

 much in the habit of depending upon the coup aVoeil to obtain their 

 average : being sure that I knew where the true meridian lay, and 

 having found by long trial that I could be more accurate in this way, 

 and especialty in respect to the dip, than by the use of instruments. 

 But after all, every geologist must be aware that all observations of 

 this kind, made in the best manner, can be only approximations to 

 the truth. In most instances, however, they come sufficiently near 

 the truth to form a good basis for reasoning : since it is large differ- 

 ences only, in the dip and direction, on which the conclusions rest. 



In strictness, when the direction is given in this report in degrees, 

 about 5 degrees should be allowed for the westerly variation of the 

 magnetic needle. 



It is only the predominant or general direction of the basset edges 

 of the strata that I have undertaken to give on the map. The preceding 

 pages of my report contain numerous local exceptions: but unless 

 these are on a large scale, as in Worcester, Goshen, &c. they have 

 not been represented. 



Dotted lines are drawn on the Geological Map of the State, (Plate 

 I,) to show where the sections, given on Plates XVII & XVIII, 

 cross the country. Section A, crosses from east to west near the nor- 

 thern part of the State. Section B, is intended to cross near the middle 

 of the State: though it deviates somewhat from a direct course, in or- 

 der to strike the granite and coal in Worcester. Section C, passes 

 through the southern part of the State; though when it reaches the 

 northeast corner of Rhode Island, it tends more to the south, in order to 

 terminate upon the famous "Plymouth Rock," which is a large bowl- 

 der of a rather peculiar kind of granite, (No. 1 133.) Section D, passes 

 from the northeast corner of the State to Boston; thence it changes its 



