SCIENCE- G OSSIP. 



opened out in a small anticlinal fold. The deposits 

 are limited in extent, and the mines are therefore 

 of no great size. The manganic ore varies in 

 quality, from an impure whitish-grey carbonate, 

 with nearly 20 per cent, of siliceous matter, to a 

 black hydrated oxide which is comparatively rich 

 in the metal. The black oxide is a result of the 

 oxidation of the carbonate, and it contains from 

 32 to 35 per cent, of metallic manganese. 



An interesting line of investigation is afforded 

 to the wayfarer in determining the number, cha- 

 racter, and position of the dike intrusions of the 

 district. The heights that rise behind Craig 

 Abermaw are crossed by considerable numbers of 

 igneous dikes, which do not appear to have 

 received at the hands of geologists the attention 

 they merit. Owing to the conditions of exposure 

 it is not always possible to trace their horizontal 



streamlet are the barren slopes of the Cambrian 

 grits ; on the other side, the many-hued Lingula 

 flags with their well-wooded sides chequered here 

 and therewith grassy knolls and patches of the 

 exquisitely blended colourings of gorse and heather. 

 The exposures of the IJngula flags and slates may 

 be traced from Aberamfra to the fifth milestone on 

 the Dolgelly road. They exhibit a series of banded 

 flags, formed by the repetition of numerous wavy 

 felspathic and siliceous layers of a light bluish- 

 grey colour, often so felspathic that the finer- 

 grained layers present the appearance of being 

 formed of spathose dust and ashes. Many of the 

 flags offer marked evidences of current-bedding. 

 The colourings of these rocks, due to the decom- 

 position of the chlorite and iron pyrites, are 

 exceedingly fine. They appear to the best advan- 

 tage on a wet day. The Lingula beds in the 



Fig. 1. Glacial Debris at Llaxaber, near Barmouth. 



extensions, but where this has been done they have 

 been found to be very persistent and of great 

 length. In most cases there are distinct evidences 

 of the meeting of the boundary faces, and many 

 opportunities are therefore afforded for studying 

 the varying phases of metamorphism. Proceeding 

 eastwards from Barmouth down the steep descent 

 of Aberamfra, the junction of the grits and the 

 Lingula beds is well marked by an ice-cold 

 streamlet which flows beneath the roadway into 

 the Mawddach. 



The characteristic surface features which mark 

 the line of demarcation between the Cambrian and 

 the Ordovician at this point serve as a useful index 

 in tracing out the line of junction, which runs 

 almost clue north. On the western side of the 



neighbourhood of Dolgelly are fairly fossiliferous, 

 but around Barmouth very few organic remains 

 have been forthcoming. This is probably due to 

 the fact that the latter have not been so thoroughly 

 overhauled as the former; but Mr. Salter's dis- 

 covery of Lingulac at Banc-y-frain shows further 

 research would probably be well repaid. Further 

 east the flags have yielded a rich series, including 

 Lingula davisii, the'crustacean Hgmcnocaris vermi- 

 cauila, and the trilobite Olenus mirrurus. There 

 is, therefore, ample work in this charming district 

 both for the fossil-hunter and for the petrologist. 



The glacialist, too, will find much to occupy his 

 energies in tracing out the directions of flow of 

 the various ice sheets which enveloped the district 

 during the Quaternary period. All of the hills 



