t 



glf» 



Outlines of the Mineralogy and Geology 



DESCRIPTION OF THE MAP. 



V 



Jfroin the preceding description, we perceive how few and sim- 



J- 



pie are tlie rocks in this vicinity. Greenstoue, Sieuite and Grey- 

 wacke form the boldest featuies in the strucliue of the country. 

 The comparatively even surface of the district, to which these ob- 

 servations are confined^ forms an important trait in its character ; 

 it may well be called a plain, with the exception of the Blue 

 hills ; and even these can scarcely he ranked as hills by the Ge- 

 olo2;ist. The eminences, which are grouped or* isolated in this vi- 

 cinity, can be considered as the undulations only oY a plain ; they 



from the north, while 

 on the south sides they are abrupt and precipitous. At present, 

 we see the external vveathereTI surface only of the masses ; noth- 

 ing has yet tempted enterprize to open the bosoms of our hills, 

 and lay bare to view their structure ; few have been explored, and 

 into th^se we have penetrated a few yards only. 



If it is unphilosophical to form plans and sections of the struc- 



where the miner has descended hundreds of 



* 



have generally a gradual and easy ascent 



of 



J 



feet, it is certainly absurd, to draw a diagram of that, where a 

 single rock has not yet been penetrated to its basis. A 

 of the district, comprehended in this map, might indeed be 

 by the aid of hypothesis^ and imajrination, and 



ade 



it miirht b 



8 



Gi 



f the rocks from the Blue hill rang 



5 north of Boston ; by i 



on th 



be shown, how the Petrosilex passes from Milton 



g 



bourhood, under the Greywacke 

 Lynn, &c. ; it midit be shown. 1 



h 



d again appears in Maid 

 the transition str 



primitive rock 



and by it midit be 



p reposes 



gr e a t 



y 



