290 A. R. Hunt — Devonian Rocks of South Devon. 



Sandquay. The western Blackstone is composed of a fine-grained 

 diabase ; while a coarsely crystallized diabase forms the southern 

 and larger portion of the islet known as the Mewstone. The Mew- 

 stone rock, or one much like it, appears on the coast between 

 Dartmouth and Blackpool Sands, and again further west inland. 

 The Blackstone (western) rock re-appears in Blackpool Valley in 

 a schistose form, where it resembles a schistose rock occurring 

 between Modbury and Aveton Giflfard ; while a porphyritic diabase, 

 recalling Sandquay, occurs in the Torcross line, near East Charleton. 

 This variety among the diabases is well matched among the meta- 

 m Orphic green rocks, where at one place we may meet with a fine- 

 grained hornblende schist ; at another, a rock in which layers of 

 felspar are the most conspicuous feature ; or, in which granular 

 felspar is embedded in a matrix chiefly composed of chlorite ; or, 

 in which the felspar grains rest in a matrix in which fibrous horn- 

 blende is prominent. 



In a quarry of greenstone, west of Winslade, a quarried block was 

 seen to be composed of two distinct rocks closely united ; one a pale 

 greyish-green diabase, the other a much darker and more schistose 

 rock which recalled some of the green metamorphic rocks further 

 south, e.g. at Bickerton. They will be described as Winslade A 

 (No. 38) and Winslade B (No. 39). In A the original augite 

 crystals ai"e well represented ; in B it is doubtful whether any can 

 be recognized. In B there is abundance of green typical chlorite, 

 polarizing a deep blue ; in A there is a corresponding mineral of the 

 faintest tinge of green, which Mr. Teall informs me is also probably 

 chlorite. The frequent association and intimate mixture of horn- 

 blende and chlorite in both the diabases and metamorphic rocks 

 is noticeable. 



It is not difficult to trace the two hoi'nblendes and chlorite from 

 the diabases into the metamorphic rocks. In a vein in the Sand- 

 quay diabase (a rock in which the original minerals are nearly 

 obliterated) we have secondary felspar associated with fibrous horn- 

 blende and very pale chlorite. At Blackpool, chlorite is intimately 

 associated with compact hornblende. At Winslade we have au 

 occasional crystal of compact hornblende and much chlorite in 

 company with a few streaks of fibrous hornblende. Near Start 

 Point we meet with a highly felspathic green rock of gneissoid 

 character containing compact hornblende, much fibrous hornblende, 

 and chlorite. This rock is an epitome of the decomposition products 

 of the Sandquay and Blackpool valley rocks, the fibrous hornblende 

 and secondary felspar of the one, with the compact hornblende of the 

 other, and the chlorite of both, being all represented near the Start. 



An interesting feature in the metamorphic green-rocks is the 

 frequent occurrence of rounded granules of felspar full of greenish 

 belonites (actiuolite?) in a matrix of what appears to be chlorite 

 and hornblende in varying proportions. In specimens from near 

 Bickerton, both north and south of the valley, as also in one from 

 Rickham Sands, the matrix is chiefly chlorite ; whereas in another 

 from near West Bolbury in which the felspar is less conspicuously 



