2 Economical Geology. 



while it exhibits all that is important to the practical man, as well as 

 to the scientific enquirer. In the first part of my Report, I shall ex- 

 plain the different formations on the map, only so far as shall be ne- 

 cessary in illustrating our geology with reference to the useful arts ; 

 reserving the most important scientific remarks to a subsequent period. 



It will be seen that I have extended the map a short distance into 

 the adjoining states. This was done chiefly with a view to exhibit 

 certain beds of ore, or other interesting minerals, which occur just 

 bevond our limits. In a statistical point of view, these are nearly as 

 important as those found within the State ; and for this reason I shall 

 notice such minerals in my Report. 



In laying down the geology of the eastern part of Rhode Island, I 

 have been much assisted by the communications of Col. Joseph G. 

 Totten, of Newport. In the geology of Berkshire, I have been greatly 

 aided by the geological map of that county, published a few years 

 since by Professor Dewey. 



It has been my intention to give to each rock, precisely that rela- 

 tive extent on the map, which it occupies on the earth's surface. To 

 do this with perfect accuracy, over an extent of more than seven thou- 

 sand square miles, would be an almost endless task : especially when 

 we recollect, that over the greater part of the surface, the rocks are 

 covered by loose soil ; so that in some instances, no rock in place 

 shows itself to the traveller, for an extent of thirty or forty miles. In 

 such cases, indeed, this stratum of sand, clay, and gravel, has been 

 exhibited on the map under the name of diluvium. Still, under the 

 most favorable circumstances for observation, the effort to give on a map 

 the exact boundaries of each particular rock, must be regarded as only 

 an approximation to the truth. Yet, for all practical purposes, such 

 approximation answers nearly as well as entire accuracy. If I have 

 not misunderstood my commission and instructions, I was to have 

 principally in view, in my examinations, practical utility ; not neg- 

 lecting, however, interesting geological facts, which have an important 

 bearing upon science. Under such impressions I have gone over the 

 State as rapidly as seemed to me consistent with the accomplishment 

 of these main objects. In attempting to construct such a map as is 

 appended, in the time that has been devoted to the survey, I am not 

 without fears that I shall be thought to have aimed at too much ; or 

 that it witt be supposed little dependence can be placed upon it. Had 

 I not previously become acquainted with the geology of nearly one 

 half the State, from my own observation, or the published accounts of 



