4 Economical Geology. 



But supposing it would be placed in some public situation, in order to 

 exhibit to the citizens the geology and mineralogy of the State, I have 

 endeavored to obtain from all the important quarries and beds, whence 

 stones are obtained for the purpose of architecture or ornament, spe- 

 cimens which would fairly exhibit the qualities and value of each. 

 About 130 of these specimens I have had polished, or smoothed and 

 varnished, in order to bring to light their real qualities. 



I have also, in accordance with my instructions, endeavored to col- 

 lect all the important varieties of rocks and minerals in the State, for 

 the use of each of the colleges in the Commonwealth : though the 

 number of specimens is not as great as in the collection for govern- 

 ment. 



In presenting a view of our economical geology, I shall first make 

 a few remarks upon the different soils found in the state, as connected 

 with the rocks over which they lie, And since it is an acknowl- 

 edged fact, that all soils had their origin in the disintegration, or de- 

 composition of rocks, it might seem easy, at first thought, to ascer- 

 tain the nature of the soil, if we know the integrant and constitu- 

 ent parts of the rock underneath it. Thus, in a soil lying above 

 granite, we might expect that siliceous sand would be the predomi- 

 nant ingredient ; next, clay with small quantities of potash, lime, 

 magnesia and iron ; because these are the constituents of granite. But 

 several causes so modify soils, as to render all conclusions of this 

 kind extremely uncertain. In the first place, the character of a soil 

 depends more, in general, upon the nature and amount of the vege- 

 table and animal matters it contains, than upon the nature of its other 

 ingredients. And in the second place, the agency of running water, 

 not merely of existing streams, but of mightier currents, to which the 

 surface has been exposed in early times, has been powerful in mod- 

 ifying the loose coverings of the rocks. This aqueous agency has 

 often covered one rock with the spoils of another ; and sometimes 

 mixed together the worn off fragments of half a dozen, and accu- 

 mulated them in immense quantities in particular districts. These 

 circumstances have rendered the subject under consideration an ex- 

 tremely difficult one ; and very few general principles have yet been 

 settled concerning it. Indeed, so far as I know, little attention has 

 been given to it in this, or other countries. Still, there is such a 

 thing as peculiarity of soil, occasioned by the peculiarity of the rock 

 from which it principally proceeded. I shall notice any peculiarities 

 pf thii kind, that have struck me, in the soils of Massachusetts ; but 



