MUSEUM OF COMPARATIVE ZOOLOGY. 2h 
a basis for the presumption that these rocks were accumulated during 
an ice epoch. 
The glacial origin of these sediments is made more probable by the 
fact that they contain a large amount of ferruginous material. My ob- 
servations on the recent drift of New England show that at a hundred 
localities, representing all the States except Vermont, the drift contains a 
large amount of such material. The conditions of glacial erosion, the 
rapidity with which the process goes on, and the absence of acids pro- 
duced by decaying vegetation in the rocks, cause glacial deposits formed 
of detrital materials originating in crystalline rocks to contain large 
amounts of iron, which under ordinary conditions of decay would be 
oxidized and borne away in the dissolved state. 
The distribution of Cambrian fossils in these beds, where they occur in 
thin layers, appears to indicate that life was present in the sea at some 
distance from this shore line, and that it occasionally, in the interruption 
of the conditions which made the rest of the beds non-fossiliferous, won 
its way to this field. Precisely similar invasions of life took place dur- 
ing the last glacial period along the shores of this part of the continent. 
Characteristics of Life. 
The organic fossils obtained from the Cambrian beds of Attleborough 
show very clearly that the section in which they lie belongs in the earlier 
divisions of that age. This is indicated by the general correspondence 
of the organic forms with typical sections elsewhere, particularly those 
in the region about the Hudson valley. It will be noted that no trilo- 
bites of the Olenellus group have been found in this section, though the 
total number of specimens of this order observed is considerable. The 
fact that one species of Paradoxides occurs in these beds appears to in- 
dicate that the fauna has rather close affinities with the Braintree Cam- 
brian horizon. It is interesting to note that this surviving member of 
the Paradoxides series is very small. I believe it to be one of the most 
minute forms which has yet been described. Although this fossil is so 
far represented by a single specimen, it affords ground for the presump- 
tion that the group was at this time imperfectly developed. 
The most interesting feature connected with these fossils is the ample 
representation of the group to which Salterella and Hyolithes belong. 
By far the greater number of the individual fossils which were found at 
the three localities belong to one or another of five species described in 
the following account of the fossil remains. Indeed, at locality No. 1, 
