186 INDICATIONS OF GLACIAL ACTION IN CORNWALL. 



afterward these large masses of granite, many of them weighing 

 from 10 to 20 tons, were brought into their present position by a 

 more powerful agent than running water ; and the carrying power 

 of land-ice is the only known natural agency by which such masses 

 of rock could have been removed so far from their parent beds. 



The Stream Tin which has been swept into our valleys, — ' 

 the drift beds which fringe our bays, — ^and the massive blocks of 

 granite and trap which have been dislodged from the hills and 

 scattered over the lands below, all tend to show that our county 

 was not exempt from those powerful agencies which modified the 

 surface of the land and impressed its seal on the landscape at the 

 glacial period. 



REFEEENCES TO PLATE I. 

 Plate I, Fig. 1. 



1. Greenstone soiL 



2. Head of large angular blocks of hornblende rock. 



3. Fine sand and loam. 



4. Pebbles of hornblende rock. Quartz (most abundant). Granite, and 



some water-worn chalk iiints, mixed with sand and with layers of fine 

 brown sand 3 to 12 inches at the bottom, about 5 feet above high water. 



Fig. 2. 



1. Soil of brown loam, 6 to 18 inches deep. 



2. Clayey loam abundantly mixed with angular shattered quartz from 6 to 



16 feet thick, but thickest in the lowest dip of the open valley under 

 Godrevy farm-house. 



3. Portions of a bed of slate much contorted, probably grooved out of the 



hill above and pressed into the sand-bed by ice action. 



4. Sandy loam from the clay- slate, mixed with siliceous sand. 



5. Ked and White siliceous sand, in fine quartz grains, partly rounded by 



water action. 



6. Boulders of blue grit, granite, quartz, vesicular trap (From St. Minver ?) 



and clay-slate, mixed with some rounded flints and sand, cemented 

 into a hard conglomerate by oxide of iron and manganese. 



