No. 9. — The Occurrence of Fossils in the Roxbury Conglomerate. 
By IlENin: T. Bure and Robert E. Burke. 
The age of the Boston Basin sediments has long been a matter 
for controversy. Two types of rock make up the mass of the sec¬ 
tion, a thick series of heavy conglomerates, and a series of compact, 
flinty slates. The former are known as the Roxbury conglomerates, 
and are usually assumed to be of the same age throughout. The 
slates are generally similar in character, but are now believed to 
represent at least two widely different horizons. The conglom¬ 
erates and much the greater portion of the slates are remarkably 
barren of fossils. In 1856 Paradoxides harlani Green was reported 
from the slates near Hayward’s Creek, Braintree, Rogers, ’56, 
pp. 27—29, 40-41. This discovery established the age of that 
portion of the slates as Cambrian. As the greater part of the slates 
in the Basin resemble those of Braintree, the whole series was 
regarded as of the same age. Within recent years Lower Cambrian 
fossils have been found in the impure limestone at Naliant, Foerste, 
’89, pp. 261—263, and at Mill Cove, Weymouth, Grabau, ’98, also 
Burr, 1900. 
In some parts of the Basin, at least, the conglomerates appear to 
underlie the slates; hence they, too, were held to be of Cambrian 
age. The conglomerates are largely made up of fragments which 
appear to have been derived from the complex of granitic rocks to 
the south, Crosby, ’89, p. 6. The granite, then, is older than the 
conglomerate. On the supposition that the conglomerate is below 
the slate, it is necessary to regard the granite as older than the 
slate, also. But the granite, as is now known, is intrusive into the 
slates of Braintree, Wadsworth, ’83, p. 27 ; also Crosby, ’89, p. 5, 
and is, therefore, later than that portion of the Cambrian series. 
The conglomerates, then, not only overlie the Middle Cambrian 
slates, but are separated from them by a great period of igneous 
action, and an interval long enough to allow the forces of erosion to 
penetrate deep into the granite mass. It is, therefore, no longer 
necessary to regard the conglomerates and associated slates as of 
Cambrian age. In the absence of positive evidence to the contrary, 
however, they are still held to be Cambrian by many observers, and 
are so mapped by Walcott in his correlation papers, Walcott, ’91, 
p. 268, and map, p. 358. 
