THE STRATIFIED ROCKS OF ESSEX COUNTY. 47 



from the Nahant locality, and east-southeast from the 

 Rowley outcrop. I have observed for several years pieces 

 of this rock, in a more or less decomposed state, in places 

 in Rockport and Gloucester frequented by fishermen, but 

 could not obtain satisfactory information as to their source ; 

 therefore, definitely locating this rock at Jeffrey's Ledge 

 is of importance as proving the extent of the lower Cam- 

 brian deposit on the coast of Essex County, Mass. I 

 have recently procured a fine specimen of this chert and 

 limestone which was hauled up on a trawl line by Mr. 

 George Parsons of Rockport ; he states that the fishermen 

 call it " horse sponge" and, as it is often perforated by nu- 

 merous worm borings and covered with hydroids and algse, 

 it certainly resembles a calcareous sponge. 

 Sept., 1890. 



