Banding of Strata. — W^ood-worth. 283 
ture parallel to the stratification resembling current or ripple 
mark, but the textures were pebbly and sandy. In the Minne- 
sota glacial deposit described by Spurr as in this rase a cross- 
banding was produced at about 45° to the true stratification. 
Of the structure described by Spurr, the writer has seen no 
examples and is therefore unable to make further comparison 
of the two cases. 
It will be noted that the simulation of the banding of met- 
amorphic schists in the lake Welden case is remarkable, and 
if the deposit existed as a firmly consolidated, slightly meta- 
morphosed rock, it might be on hasty examination mistaken 
for an ordinary deposit with its banding induced by the pro- 
duction of new minerals. Where metamorphism and the pro- 
duction of micaceous minerals take place without shearing as 
in the quartz-albite-biotite rock of the "Devil's foot ledge" in 
the Carboniferous of Kingstown, Rhode Island, the secondary 
mica may lie in the original planes of stratification, including 
those of the cross-bedding. ^Moreover, it is conceivable that 
the metamorphism of a bed like that at lake W'alden under 
static conditions without defonnation might lead to the reten- 
tion of the essential arrangement of the original particles. The 
writer is not aware, however, that any known mica-schists or 
quartz-mica-schists exhibit evidence of this original distribu- 
tion of their mineralogical components. 
An analogous but not homologous structure exists in the 
diagonal fissility of \'an Hise in certain sheared and mineral- 
ized sediments. Thus in the carboniferous gneissoid sand- 
stones of Prudence Island in Xarragansett Ray, these bands of 
compact mineralized layers of arenaceous sediments alternate 
with thicker layers of finer sediments less mineralized but be- 
set by open planes of diagonal fissility inclined about 45° to the 
bedding, this secondary structure occupying relatively to the 
mineral banding the ]X)sition held by the original fiedding 
planes to the micaceous banding in the glacial deposit above 
described. 
