PREFACE. 



The law, under whose authority the reports of the Geological Sur- 

 vey are being published, determines the character of one volume, 

 w-hich, from its nature, will most appropriately form the initial vol- 

 ume of the C(^mpleted series. But as it involves general conclusions 

 that can only be arrived at after the completion of field work, its ap- 

 pearance must be delayed until that work is accomplished. It was 

 not deemed advisable on this account, however, to defer the publica- 

 tion of such portions as could be finished, and the present volume, 

 although nominally the second of the series, appears first in the order 

 of time. 



Although its size has been expanded beyond what was originally 

 intended, and a large portion of its matter printed in a smaller type 

 than is desirable, it has been found impossible to include all the ma- 

 terial that has been gathered relating to the regions reported upon, 

 and a considerable amount of manuscript relating to each of the dis- 

 tricts has been necessarily omitted, and other portions condensed to 

 an undesirable brevity. It is believed, however, that, notwithstanding 

 this, a creditable degree of thoroughness and fullness has been attained, 

 and that, by the assistance of the ample maps and profiles that accom- 

 pany the volume, an adequate knowledge of the structure of any 

 locality may be obtained. 



The law authorizing the survey requires the construction of a sin- 

 gle map upon which shall be represented all the geological forma- 

 tions of the state. A map based upon a scale of fifteen miles to the 

 inch, is the smallest upon which this can be successfully accomplished, 

 and this fact has determined the form and dimensions of the accom- 

 panying atlas, whose sheets have the size requisite for such a map. 

 A scale of three miles to the inch is the least that is at all adequate 

 to the proper representation of the detailed mapping of the formations, 

 and this scale has been uniformly adopted . for the more elaborate ge- 

 ological maps. It was found that the surface of the state, on this 

 scale, was readily and economically divisible into rectangles of the size 



