Satles. — The Squantum Tillite. 



PLATE 10. 



Pebbles from the tillite. 



Beginning at the upper left hand corner the pebbles from left to right are: — 

 quartzite pebble from Roslindale showing subangular shape and fracturing; 

 granite pebble from Roslindale showing subangular shape and concave frac- 

 tures; melaphyre pebble from Squantum Head showing bevelling and striae; 

 quartzite pebble from Franklin Field shown to better advantage in Plate 11; 

 quartzite pebble from Roslindale showing bevelling, faint striae, and concave 

 fractures; here an attempt was made to show ice bevelling on both sides of a 

 central ridge, the ridge is indistinct in this picture. The last specimen was 

 found by Dr. Arthur Keith of the United States Geological Survey and con- 

 sidered by him at the time as of glacial origin. 



