GEOLOGY. 41 



these localities, there is a great variety, and some spe- 

 cimens receive a beautiful polish, but have not yet been 

 wrought to any extent. Many of the paving stones in 

 the streets of Boston are porphyry, which are quite 

 distinct after a rain. A part of the Andes mountains 

 are said to consist of porphyry, but the rock is not 

 common. 



Amygdaloid somewhat resembles porphyry, as it con- 

 sists of a homogeneous base, and imbedded crystals. 

 But the base is less various, and usually softer, than that 

 of porphyry, and the imbedded minerals of an oval or 

 spheroidal form, somewhat resembling almonds in shape, 

 and hence the name of the rock. 



This, like the rock last mentioned, is sometimes used 

 for ornamental purposes, as some varieties are capable 

 of a good polish, when they exhibit a beautiful com- 

 plexion and surface. 



In Brighton and Hingham, in the vicinity of Boston, 

 this rock is found in large quantities, and in small quan- 

 tities in the vicinity of New Haven, and a few other 

 places. It is, however, less common and less abundant 

 than the rock last mentioned. 



The strata of rocks above mentioned and briefly de- 

 scribed, are the principal materials which constitute the 

 mountain masses, and loose fragments or bowlders upon 

 our globe, from which soils are supposed to be formed, 

 and of whose character they certainly partake. Another 

 occasion may admit of a fuller and more accurate de- 

 scription. 



At present we can only add a few reasons why geolo- 

 gy should be universally introduced as a branch of 

 common education. The substance has already been 

 published in the Journal of Education. 



1. It is nearly allied to geography. The connexion 

 and distinct provinces of these two sciences, have 

 already been pointed out in the introductory remarks of 

 this number. From that view it is believed, many will 

 be ready to acknowledge that the claims of this science 

 to becoming a subject of common school instruction, 

 are equally strong with those of geography, and in 

 some points superior. 

 VOL. i. NO. ii. 4* 



