164 DREDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION: 



raised a fine-grained granite also with Iwth lirown and silvery 

 mica. 



There is evidence that the rock hottom at A. 78, A. 79, is Triassic. 

 While the gneiss from A. 86 (354/1), | mile N.W. of Eddystone, was 

 a large angular slab, with one face of apparently clean fracture. 



Thus on this class of evidence granite, gneiss, and trias have alike 

 been found in situ. 



Another feature that argues strongly for a rock being near its first 

 home is the angular or sub-angular form occasionally presented ; especi- 

 ally is this form of evidence of value when the stone is such as will 

 readily suffer from transport. 



A. 100 (354/2), 2 miles S.W. of Eddystone, gave large stones, a thin 

 slab of variegated Triassic sandstone, a rather thin slab of buff Triassic 

 sandstone, and a thin piece of red marl, all angular and practically un- 

 worn. Such rocks as these could not travel without great wear. 



M. 19. S. 28^ W. Edd., 23-3 miles yielded large square blocks of Eed 

 Triassic Sandstone. 



M. 14. S. 17° W. Edd., 29 '8 miles, yielded thin sharp slabs of Liassic 

 limestone. 



There are other similar instances. Evidence of this type again 

 demonstrates practically in situ exposures of Trias, and in this case of 

 Lias as well. 



A third clear indication of localisation is when the adjacent sea- 

 bottom yields rocks of the same class and type as shore exposures. 

 The sea-bed off the Bolt and around the Eddystone affords instances. 



To some extent coupled with this is a fourth strong class of evidence 

 — the restriction of the occurrence of a given type rock to areas with 

 definite boundaries. Thus the Bolt and Prawle schists vary in type as 

 we proceed southward along the sea-bed. The Eddystone and Hand- 

 Deeps gneisses are restricted to the immediate neighbourhood of the 

 reef ; in A. 102, S. Edd., 2^ miles, the gravel contained no Eddystone 

 reef material, although in A. 87, N.W. by N. Edd., 1 mile, 87 % of 

 it is derived from the reef. It will presently be seen how, on a much 

 larger scale, the New Eed Sandstone series is definitely bounded. Thus 

 at M. 27, S. 19° W. Edd., 18 3 miles, there is a representative series of 

 Triassic rocks ; at M. 29, S. 14° W. Edd., 198 miles, these are entirely re- 

 placed by the maris of the passage-beds to the Ehaetic. The distance 

 is under two miles. 



Another, the fifth, possible proof that a rock is near its point of 

 origin applies in but a few cases. An example will best explain it. 

 On all the preceding arguments we may decide that the gneiss of the 

 Hand Deeps is practically in situ. 354/3b is a red conglomerate of the 



