CLARK: NEW FOSSILS FROM NEAR BOSTON. 475 
This fauna shows very close affiUation with that of the Lower 
Cambrian rocks at Nahant and Attleboro, Massachusetts, and 
also of Washington and Rensselaer Counties, New York. In the 
small size of the specimens it especially resembles the fauna of 
the last-named region, whereas the abundance of fragments of 
Callavia indicates a connection with the fauna of North Wey- 
mouth, which is the only locaHty near by where that genus has 
previously been found. The outcrops of Low^er Cambrian rocks 
around Boston are few in number and limited in extent, but, 
taken as a whole, the fauna is a homogeneous one and is not 
radically different from that of eastern New York, 
The discovery is of particular interest in suggesting an undis- 
covered locality of fossiliferous Lower Cambrian rocks at no great 
distance from Revere Beach. The pebbles were all found within 
a mile of the southern end. All of the materials of the beach are 
of glacial origin, distributed along shore by marine currents and 
waves, and our pebbles were probably deposited by the ice 
approximately where they are now found. The glacier advanced 
over this part of Massachusetts from the northwest, so that we 
should look in that direction for the Lower Cambrian outcrops 
whence these fragments were derived. Sears, in his volume on 
the Geology of Essex County, has plotted dozens of localities at 
which Cambrian rocks outcrop, some substantiated by fossils. 
There are some recorded in Saugus near Breakheart Hill, rather 
too far east for our purpose. Much ci-iticism has been launched 
at Sears of late because some of his localities do not seem to be 
where he mapped'them, but it should be remembered that no one 
since has spent one-tenth of the time which he did exploring the 
Essex County ledges. The discover}- of these pebbles strengthens 
the view that the country to the north and northwest holds 
further outcrops of Cambrian rocks which will doubtless be found 
by later ambitious seekers. 
In the notes which follow it has not been thought necessary to 
submit a complete bibliography with each species. Where it has 
been discussed by Grabau in Crosby's Geology of the Boston 
Basin, a page reference to that article is given which will lead the 
reader to a nearly complete bibliography up to 1900. A supple- 
mentary bibliography has lieon adih^l on page 479. 
