160 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
of the tillite and transition-beds and the uppermost part of the slate 
formation. The strike here is N 12° E, and the dip 70° N. The 
tillite exposure proper is very small and little can be said of it. The 
matrix of the tillite is sandy. The pebbles and boulders are angular, 
subangular, and rounded. The transition-beds are very much like 
those at Squantum Southeast:—large boulders and slate fragments 
mingled in an unstratified mass, with here and there thin layers of 
sandstone. An ice-rafted boulder was extricated from the slate, and 
many more may be seen. 
Melaphyre appears about fifteen feet below the tillite, but whether 
as a flow, dike, or sill has not been satisfactorily determined. 
Crosby studied this locality some years ago and wrote (1894, p. 249) 
as follows concerning the tillite: — “The pebbles are of all sizes up 
to a yard or more in diameter, the largest observed being a boulder 
of coarse granite over 5 feet in length. Furthermore the various 
sizes are jumbled together promiscuously without evident assorting 
or stratification, looking not unlike an indurated till or boulder clay.” 
Crosby discovered some exotic limestone here, which he thinks came 
from the north. He did not prove his conclusions, however, on 
this point (Crosby, 1894, p. 265-266). 
Cleavage is well marked. 
Criteria found: — A, B, C, D, F, J, L, M, N, O. 
Locality — Arnold Arboretum. While the proof of this paper was 
in press, I discovered a large tillite locality in the Arnold Arboretum 
north of Peters Hill. It is the ridge covered by evergreens on the 
eastern margin of the Arboretum grounds. This is along the same 
strike as Locality 3, but farther northeast. No contacts with other 
beds have been seen, so it is impossible to obtain strike and tip. 
Criteria observed during one visit: — A, B, C, D, J, M. 
REVIEW OF LOCALITIES WITH CRITERIA. 
The list of localities on the following page with the criteria of tillite 
found at each, are arranged as nearly as possible according to the 
extent of outcrop, and favorable conditions for search. 
The list below shows that where there is ample opportunity, abun- 
dant criteria are usually found. It must be noted that a thorough 
examination of some outcrops has been impracticable as yet, owing 
to location in private grounds or cemeteries. Other outcrops are so 
limited in extent that they show only the presence of the formation. 
