Cambrian Organisms. 387 
They consist of graptolites of the genera Bryograptus, 
Tetragraptus and Dichograptus, with a large Orthis and a 
Cyclognathus 
The physical history of this part of Canada, in Cambrian 
times as shown by the Cambrian terreins in southern New 
Brunswick, was briefly as follows : 
The basal series is marked throughout by the waning 
effects on its sediments of the eruptive activities of the pre- 
ceding age. The series is variable in thickness, the con- 
glomerates have some closely cemented breccias as well as 
the ordinary rubbly conglomerates of sedimentary origin. 
Occasional thin beds of felsite and petrosilex are found, 
and the finer sediments have a strong green or red tint, 
.and are more or less charged with iron. 
In the St. John group, the rocks of Division 1 show a 
gradual deepening of the sea without disturbance; and 
without any trace of eruptive activities after the first few 
bands were laid down. 
When the second division of the St. John group was being 
deposited, the sea-bottom again came up to the surface, and 
was awash, or was under a thin covering of sea-water 
throughout this stage. 
At the beginning of the third stage, the land again sank, 
and continued under a considerable depth of water through- 
out the whole of this age, as we see from the great body of 
fine dark grey slates, which form the bulk of the measures 
of this division. 
Finally the sea-bottom sank deeper still, and in tranquil 
waters, comparatively free from currents, lived the grap- 
tolites which we now find buried in the soft carbonaceous 
mud (now changed to slate) found to have been deposited in 
this region after the close of Cambrian time. 
