258 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
possible that such may have existed and have been removed by 
the same erosion that stripped the disintegrated material from the 
surrounding country in the early part of the deposition period. It, is, 
however, fairly certain that, during the latter part of that period, moun- 
tains existed to the northwest of the Boston Basin, as shown by the 
muscovitic material in the Dighton Conglomerate, and these may have 
been represented in subdued form before the deposition of the Carbon- 
iferous strata began. The combination of arkose and of red strata 
; in the lower part of the series indicates that the climate must have been 
cool and the rainfall moderate or scanty. Thus a mountain region 
of moderate elevation or a land area of greater or less extent must 
have intervened between the region now occupied by the Carbonif- 
erous strata and the sea. 
The deposition of the sediments was inaugurated by changes that 
permitted rapid removal and deposition of the decayed material, 
then covering the entire region, and the vigorous attack on the fresh 
subjacent rock. These changes may have been partly climatic but 
probably they were chiefly orogenic; for at the close of the deposition 
period, as recorded in the Narragansett Basin, land areas must have 
existed both to the northwest and the southeast, sufficiently high to 
have furnished the grades necessary for the transportation of such 
coarse material as is found in the Dighton and Purgatory Conglom- 
erates. Doubtless these elevations were of sufficient altitude to sup- 
port active glaciers. There are many indirect evidences that such 
was the case. 
The orogenic movement may have been simply differential uplift, 
whereby certain areas became subject to vigorous erosion, while 
other regions received extensive deposits, or it may have been such 
an uplift accompanied by faulting. The evidence of probable bound- 
ary faults in the Boston and Norfolk Basins and the occurrence of 
contemporaneous igneous activity, so marked in the Boston and Nar- 
ragansett Basins, tend to show that block faulting may have occurred 
during the deposition of the sediments and may perhaps have been 
responsible for the relief that permitted such vigorous erosion. The 
somewhat uncertain evidence furnished by the coarse conglomerate 
along the south base of the Blue Hill Range is favorable to this view: 
At least two systems of block faults can be recognized throughout the 
region, having respectively north-south and east-west trends. The 
north-south faults of Pondville are seen to be younger than the folding 
of the sediments, therefore younger than the period of deposition 
but no evidence is known to the writer that proves the east-west faults 
ie m 
