MUSEUM OF COMPARATIVE ZOOLOGY. 21 



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. 



Characteriacics 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, 



