166 GEOLOGY AND MINERALOGY OF NEWBURY. 



properly be called an iron ore, and its decomposition in 

 one or two places observed by me has yielded a red 

 ochre. 



3. Diorite. This rock is laid down on Crosby's map 

 as covering a large part of Newbury. It is the gangue of 

 the argentiferous galena. Composed of feldspar and 

 hornblende, generally in a finely divided, and sometimes 

 in an impalpable mixture, it is very hard. 



Diorite is a convenient term to describe all that class 

 of rocks formerly known as trap and greenstone. Like 

 granite and felsite, it is not the name of a single distinct 

 species, but of a family having relationship on one hand 

 to felsite, and on the other to granite and hornblendic 

 gneiss. 



4. Limestone. The magnesian limestone of Newbury 

 is the best known of its geological formations. 



In colonial times quarries of it were worked at the 

 localities known as the "Devil's Den" and "Devil's Basin.'' 

 In his diary of remarkable events uuder date of 1697, 

 Judge Sewell records the discovery by Ensign James 

 Noyes, of the beds of limestone in this town at the local- 

 ities just named. The discovery created great excite- 

 ment, as hitherto clam and oyster shells had been the 

 only sources of lime, and great difficulty had arisen in 

 consequence. 



This appears to have been the first limestone discovered 

 in Massachusetts, and so valuable was it held to be that 

 restrictive regulations for its use were adopted and a com- 

 mittee appointed by the town to enforce them. 



In the first century after its discovery, quantities were 

 exported, though from the size of the excavations I should 



