SAYLES: THE SQUANTUM TILLITE. 151 
“The exposures at this place are large blocks which show occasional 
well marked, laminated strata of a fraction of an inch to two feet in 
thickness. Since these beds all dip vertically and strike in the same 
direction, I believe that they are practically in situ. Alternating 
with these strata are layers that absolutely lack any evidence of water 
sorting and water deposition. 
“The sorted layers, sometimes of uniform width for many feet, 
consist of mudstone and sandstone. In the thickness of the entire 
cliff section they may represent 15 or 20 percent. The unsorted 
layers contain angular and irregularly shaped fragments of pinkish 
granite (the species so common in the Roxbury conglomerate), gray 
quartzite, greenish felsite, and dark green, chloritized melaphyre. 
There are some rounded pebbles. These fragments and pebbles are 
very variable in size. They range from grains of quartz and feldspar 
ze to zs of an inch in diameter to large boulders, the largest seen being 
four feet long. They are contained in a compact, greenish gray paste 
or matrix which comprises 50 to 75 percent of the bulk of the rock. 
Having no parallel structure of any sort — bedding or schistosity — 
the paste breaks with an uneven fracture. Although the term 
‘tillite’ is applicable to the whole section, I use it here with reference 
only to the unstratified, unsorted portions. My thin sections were 
cut from a hand specimen of this tillite. 
“When examined with the microscope, the finer part of the rock is 
found to be composed of minute grains of quartz and feldspar, very 
small laths of sericite, and a highly refracting, granular substance, 
uniformly distributed, which is probably epidote. The quartz and 
feldspar are so fine that little can be distinguished. The sericite laths 
show a tendency to parallel orientation, thus indicating some shearing 
in the rock, but not enough to produce a visible schistosity in the hand 
specimen. The laths are small and of nearly uniform dimensions. 
The paste may be said to consist of particles having the same size as 
these laths, or smaller. This mica constitutes between 20 % and 
25 % of the matrix. 
“Tn the paste are scattered grains of quartz and feldspar and small 
fragments of granite, quartzite, and melaphyre, as seen in the hand 
specimen. ‘These grains and fragments are usually angular. The 
larger quartz particles exhibit slight wavy extinction and some crack- 
ing, and also fine peripheral granulation accompanied by the marginal 
insertion of sericite laths, characteristic of the early stages of dynamic 
metamorphism. Of the feldspar grains, examples of orthoclase, micro- 
cline, microperthite, and plagioclase (albite to oligoclase) were de- 
