272 C. A. SUSSMILCH AND T. W. E DAVID. 



slowly settled down in winter time, while the lake was 

 frozen over and there was no melting of ice on the neigh- 

 bouring glaciers to bring about the flow of water necessary 

 to transport the coarse material. The thickness of each 

 season's deposit (i.e. a pair of layers) is somewhat variable, 

 but averages about two-thirds of an inch, so that the 200 

 feet of these varve shales which occur at Seaham must 

 have taken about 3,000 years to deposit. Layers from 

 four to six inches thick and consisting of fine material only 

 occur, but are few in number; similarly some thicker layers 

 of coarse material only also occur. Occasional isolated 

 pebbles ranging from half an inch to three inches in diameter 

 are found in these varve shales, and occasionally also a 

 regular 'pocket' of such pebbles is found, the pockets 

 ranging up to several feet in diameter. Such a 'pocket' 

 of pebbles occurring in such exceedingly fine-grained thinly 

 bedded strata m ust be due to the melting of a small stranded 

 ice-berg dropping its pebbles on the one spot as it melted. 

 The isolated pebbles would be due to the melting of drifting 

 icebergs and the dropping by them of occasional pebbles 

 as they floated over the surface of the lake in which the 

 shales were deposited. 



At intervals in the varve shales as shown in fig. 1 there 

 occur layers which are strongly contorted, similar to those 

 described by Sayles from the Squantum Beds. These con- 

 torted layers range from a few inches up to four feet in 

 thickness and display in miniature every type of Alpine 

 folding as shown in Plates XXIV, XXVI, and XXVII. A 

 bed which is contorted in one part may fade out into a part 

 which shows no contortion at all, while the contorted layers 

 themselves are interstratified between perfectly regular 

 unfolded layers. The whole evidence suggests that the 

 contortion is contemporaneous and is due to the stranding 

 of floating masses of ice, or perhaps in some cases to the 



