166 DEEDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION : 



a variety that by no means in all cases involves difference of 

 origin. 



For the moment all granites and associated rocks which may have 

 had a Dartmoor origin are excluded from consideration ; these are 

 extremely few in number. The first part of this paper must be left 

 to speak as to the variety of the plutonic rocks met in these dredgings. 

 But here such slight evidence of relative age as can be adduced may 

 well be considered. Gneiss is known to occur at the Eddystone in 

 situ ; it occurs also at the Hand Deeps and the East Eutts, and not- 

 withstanding the doubt thrown upon the fact, I am inclined to consider 

 that the ' Shovel Eeef specimen ' was, indeed, obtained near Plymouth 

 Breakwater. This has been rendered the more probable by discoveries 

 made since the time when Mr. A. E. Hunt, on evidence that warranted 

 him in all fairness, challenged the fact. 



We now know, as we did not then, that gneiss occurs at the East 

 Eutts, and chlorite schist off Stoke Point, in each case without any 

 trace of their presence being visible on shore. 



Gneiss also occurs at M. 36, M. 9, M. 16, and M. 25 stations, which all 

 lie in a narrow north and south strip, extending from 17"5 miles 

 S. 37° W. from the Eddystone to 23 miles S. 24° W. from the Eddy- 

 stone, a strip not quite three miles broad. M. llx and M. 20g might 

 also be classed as gneiss, and would somewhat broaden the patch 

 referred to. In any event there is a certain localisation about these 

 associated rocks. The writer has always hitherto leant to the hypo- 

 thesis that the Eddystone gneiss was of Archaean age. From the 

 features of similarity the gneiss from this area would presumedly be 

 of the same formation. And there is an interesting piece of evidence 

 which at least tends to indicate age. A number of grit stones have 

 been dredged from various parts of the area examined (see p. 142). 

 Among these is M. 9d, and that rock contains as derived fragments 

 particles of just such gneisses as occur in the neighbourhood. 



It is impossible to correctly date the grits, which may be either 

 Carboniferous or earlier, perhaps more probably the latter. 



Turning next to the schists. One of the most interesting finds was 

 off Stoke Point, where chlorite schist is not uncommon (see p. 139), 

 This brings the Bolt series many miles west. For the rest, the petro- 

 logical notes give all the useful information. 



As bearing on the age of some of the plutonic rocks we have to 

 observe that there is an area over which slates are common which 

 show evidence of contact metamorphism. The northernmost point of 

 this area is M. 11, S. 26" W. Edd., 17-8 miles, the southernmost is M. 24, 

 S. 24° W. Edd., 22-5 miles, about five miles long ; tlie patch is from one to 



