300 Scientific Geology. 



that Mr. Eaton proposes to give the two varieties distinct names, 

 founded entirely on their mineral characters, that in the eastern 

 part being decidedly the oldest. I think, however, that in con- 

 sidering this question, we ought to leave out of the account every 

 bed of limestone occurring in the gneiss and mica slate of the 

 Hoosac range ; since this is unquestionably the oldest of the saccharine 

 limestone. And perhaps the remaining portions of this rock may be 

 found to belong to a single deposit. At any rate, I regard it as prema- 

 ture to assign a distinct name to any part of this limestone range, until 

 one part can be proved to have a different position, in relation to other 

 rocks, from the other. For after what Dr. Maccullock has written 

 on this subject, in his Geology of the Western Islands, and in his Sys- 

 tem of Geology, it seems to me evident that mineral characters alone 

 can rarely determine even the class to which limestone belongs. 



Notwithstanding the difficulties which I have suggested to the hy- 

 pothesis under consideration, I know of no better explanation of this 

 anomalous case. I am sustained in this opinion by that of Dr. Em- 

 mons, of Williams College, whose acuteness of observation and ac- 

 curacy of discrimination in the various departments of natural his- 

 tory, are well known. It is to be hoped that either he, or Prof. 

 Dewey, whose local situations and geological experience give them 

 great facilities for examining the point, will ascertain the true state 

 of the case, and thus solve an interesting geological problem. Since 

 my attention has been called to it, I have not felt justified by my com- 

 mission in devoting the time and expense requisite to its solution : 

 since the examinations would delay this Report another year. 



The Berkshire limestone passes through numerous gradations of 

 texture and color, from the snow white, coarsely granular and crys- 

 talline variety in Adams, to the white almost sandy dolomite of Shef- 

 field, and to the dark gray almost compact variety in Williamstown, 

 and to the variety even darker of West Stockbridge. The specimens 

 that have been polished (Nos. 428 to 442,) will show the principal 

 varieties of marble thence derived. The clouded varieties, although 

 very rich, are less esteemed as marbles, I believe, than the snow 

 white, on account of their liability to be shaky. This tendency re- 

 sults from the nature of these varieties; composed as they seem gen- 

 erally to be, of limestone and argillaceous slate. The different va- 

 rieties are frequently interstratified at the same quarry. 



A large proportion of the Berkshire limestone, especially along 

 its western borders, is the magnesian. In Williamstown this occurs 



