242 A. R. Hunt — Devonian Rocks of S. Devon. 



having failed in liis search for evidence of their pre-Carabrian age. 

 In 1883 Prof. Bonney, without much hesitation, prochiimed ihe 

 Archeean age of these troublesome rocks. 



Under these circumstances there seemed nothing for me to do but 

 to continue collecting facts, and to await the issue of events. 



In 1887, 1888, and 1889, Mr. A. Somervail published three papers 

 in the Transactions of the Devonshire Association, in which he 

 suggested that the chlorite schists might be the representatives of 

 the Devonian diabases which appear on the coast line of Start Bay, 

 and in the neighbourhood of Dartmouth. 



Early in 1891, Mr." W. A. E. Ussher was good enough to allow 

 me to accompany him on two occasions when mapping the Devonian 

 rocks between Dartmouth and Slapton Sands. Being much impressed 

 by the many obvious analogies between these rocks and the meta- 

 moi'phic rocks further south, I determined to examine and compare 

 as many varieties of the two sets of rocks as I could obtain. 



My self-appointed task, then, has been to endeavour to ascertain 

 what affinities, if any, can be detected between the metamorphic 

 rocks of South Devon and the slates grits and volcanic rocks which 

 lie to the northward of them ; the green rocks being compared with 

 the volcanics, the mica-schists with the slates, and the quartz-schists 

 with the fine grits or sandstones. 



At fi.rst sight the quartz-schists and grits seemed the least pro- 

 mising of the different rocks selected for comparison ; but on Mr. 

 Harker finding detrital tourmaline in one of the Devonian grits, and 

 the same mineral being subsequently detected by myself in a quartz- 

 schist from near Start Point, these siliceous rocks took a foremost 

 place in the investigation. 



The Quartz-Schists and Grits. 



A geologist examining the classical area of Devonian rocks which 

 forms the northern shore of Torbay between Hope's Nose and 

 Hesketh Crescent, will not fail to notice the frequent interbedding 

 of slates and grits (the latter often in bands too thin to be dignified 

 by the name of sandstone), and that both rocks are often more or 

 less micaceous. 



A slice of a brown sandstone from the quarry on the path east of 

 Kilmorie is seen in the microscope to be composed chiefly of fine 

 grains of quartz, of which the larger average about -^^o inch in 

 diameter, some of them being splinters with angles absolutely 

 unaffected by attrition or solution ; among these may be noticed an 

 occasional flake of white mica, a few scattered fiagments of tour- 

 maline, and two or three grains of triclinic felspar. 



Another specimen from the same quarry is a fine hard lead- 

 coloured sandstone bedded in well-marked laminas. which determine 

 its fracture under the hammer ; the surfaces of these planes of 

 fracture being highly micaceous. 



The bands of grit between slates are sometimes crossed by quartz- 

 veins which do not invade the adjacent slates. 



In the cliffs at the north-east end of Slapton Sands we meet 



