A. B. Hunt — Oranitoid Fragments in Culm. 257 



(4) Strongly marked strain shadows in quartzes, more rarely 



seen in felspars. 



(5) The fluid inclusions in quartzes very minute, with absence of 



chlorides. 



(6) Absence of tourmaline. 



Exception may perhaps be taken to No. 4, as strain shadows are 

 strong in the veins of granite which intersect the Culm grits. But 

 these are peculiar. The only case of equally strong strain shadows 

 within the borders of Dartmoor known to me is shown in a slice 

 from the neighbourhood of Brent Tor. But that locality may also 

 be said to be peculiar. Taking texture alone, it would not be easy 

 to find a Dartmoor granite as fine in grain as the fragments from the 

 Culm conglomerate ; and so far as my experience goes it would be 

 extremely difficult to find a Dartmoor rock without either a trace of 

 tourmaline as a mineral constituent or a trace of chlorides caught 

 up by the quartzes. 



I believe General McMahon, after considerable experience of 

 Dartmoor, has observed that at the time of writing he had never 

 seen a specimen without tourmaline. I may say that I have never 

 yet examined a slide from Dartmoor which did not reveal traces of 

 salts crystallized in the fluid inclusions, though in one or two cases 

 these almost eluded detection. As a rule, wherever there is tourmaline 

 in abundance in a Dartmoor crystalline rock there will also chlorides 

 be found in abundance. Not so in the contact grits ; there tourmaline 

 seems to abound without the chlorides. 



The difi'erences between the Culm granite fragments and the 

 Dartmoor rocks are sufficiently remarkable, but still more so is the 

 fact that none of the innumerable varieties of Dartmoor rocks and 

 minerals have been detected in the Culm conglomerates and sand- 

 stones. I have never seen a grain of felspar, mica, or quartz in the 

 Culm rocks of which one could say, that it probably came from 

 Dartmoor. 



"While engaged in examining the Culm granitic fragments 

 I received in due course the Abstract Proceedings of the Geological 

 Society for February, 1899, containing a notice of Mr. A. E. Salter's 

 paper on Pebbles of Schorl Rock from the South- West of England, 

 and Professor Bonney's observation that Mr. Salter's pebbles 

 resembled certain tourmalinized sedimentary rocks which occurred 

 in the South- West of England and in the Budleigh Saltertou 

 conglomerate. This paper, coming when it did in the nick of 

 time, interested me greatly, and Mr. Salter was kind enough to 

 send me a few scraps of his pebbles. In one of them, to my great 

 surprise, I recognized my anomalous schorlaceous rock from the 

 Labrador breccia. Mr. Salter then favoured me with a sight of his 

 slides. They seemed to me to show that one great Devonshire 

 problem had been solved, viz., the origin of some of the doubtful 

 fragments of the New Red breccias. 



By diagnosing Mr. Salter's pebbles. Professor Bonney had cleared 

 up a difficulty I had despaired of ever seeing explained. Of course, 

 it is easy to be wise after the event, so it was no surprise to find 



DECADE IV. VOL. VI. NO. VI. 17 



