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 tishermen, 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 hyclroids and algae, 
it certainly resembles a calcareous sponge. 
Sept., 1890. 
