72 jvik. e. n. worth on the igneous constituents of the 



is not meant to imply that there is any absolute natural assortment ; 

 but that the range decreases, from materials varying between boulders 

 and sand, to materials in which the larger pieces would fairly be called 

 gravel. 



This recital marks out the purport and scope of the present 

 inquiry. 



Investigation. 



In the preparation of this paper special examination has been 

 made of the breccio-conglomerates near Crediton, Exeter, Heavitree, 

 Exminster, Dawlish, and Teignmoath, with specimens of the con- 

 tained rocks collected at other points — to the number, in all, of 

 several hundreds, indeed thousands. 



Generally speaking, the largest fragments occur, as already noted, 

 at and near Teignmouth ; and many very interesting examx)les may 

 be seen there built into walls near the sea. Especially prominent 

 also are the boulders in the Dawlish valley. Blocks occur ranging 

 to four and five feet in diameter. Around Teignmouth and Dawlish, 

 too, the breccias and conglomerates are most varied in their com- 

 position, and contain the largest proportion of granitoid rocks. 



The constituents of the Exminster conglomerates come next in 

 size, and frequently range up to four or five inches in diameter, 

 occasionally more. The granitoid character is also well preserved. 



At Heavitree the same leading associations are fairly prominent, 

 but the fragments show a smaller average, and the proportion of 

 immediately recognizable granitoid examx:)les is smaller also. 



In the immediate Crediton district granitoid constituents, though 

 present, are not prominent, although at points igneous fragments 

 abound. They are plentiful, however, to the west, in the strip of 

 Trias ranging along the north of Dartmoor, especially near North 

 Tawton and Sampford Courtenay. 



The igneous fragments in the Torbay conglomerates diminish in 

 size and importance southward from the Teign. They are less con- 

 spicuously granitoid, and are frequently better rounded than their 

 sedimentary associates. 



In the Triassic outlier at Slapton, if we may draw any conclusion 

 from the modern beach, granitoid pebbles must have been fairly 

 common, since there are plenty of well-characterized examples on 

 Slapton Sands which could not have been brought thither by any 

 modern river, but may well be Triassic waste. 



The following is a complete list of the various kinds of igneous 

 and altered rocks noted. JVIost of them are re2">resented by numerous 

 examples and occur at different points, and very few can be regarded 

 as rare. 



I. Granites. 



1. Coarse-grained granite with porphyritic felspars, partly kaoli- 

 nized. Differs from ordinary coarse-grained Dartmoor granite 

 only in its reddish colour, though here, as in the dark-red 

 porphyries, the kaolinized felspars are white. I am indebted 

 for this example to Mr. Vicary. 



