252 



Davies — Phosphate Bed at Llanfyllin. 



As this bed occurs in a rich geological district with which I am 

 familiar, I may be allowed, perhaps, to direct the reader, as briefly 

 as I can, to a few points of geologic interest connected with it. 



The bed occurs in the midst of what I have elsewhere described 

 as the middle and principal band of Bala limestone ; it was first 

 discovered at Cwmgwynnen, on the road leading from Llanrhaiardar 

 to Llanwddyn, and has since been traced as a continuous bed south- 

 west of this spot about two miles, and north-east about the same 

 distance to Penygarnedd, where, following the course of the lime- 

 stone, it bends sharply to the south, in \hB hill Llechwed Llwyd. 

 I am informed that it has also been found in several places in the 

 broken lines of Bala limestone north of the town of Llanfyllin. 



KivEB Tanat. 



4 5 6 7 8 



Fig. 2. Section of strata at Cwmgwynnen mine, north-west of Llanfyllin. 



] and 2. 

 3. 



Dark blue limestone and shales, Orthis elegantula, Lingula longissima. 

 Dark green schists, with Echinosphserites, Caryocystites ; passing into blue limestone 

 ■with Phragmoceras arouatum, lUaemis Davisii. 



4. Black phosphatic limestone, full of concretionary masses, and iron j)3mtes, ■with 



Orthis flabellulam, O. porcata, lUaenus Davisii. 



5. Black Phosphate bed, eighteen inches thick. 



6. Layer of Kaolin, passing into solid felspar, sprinkled with copper pyrites. 



7. Solid limestone, containing much phosphate. 



8. Sandy ash, containing casts of Pterinea. 



9. Compact Calcareous ash. 

 A. B. Levels. 



It has been worked somewhat extensively at Cwmgwynnen, and 

 here it may be studied best. It is black in colour, has an average 

 thickness of about fifteen inches, and occurs in a hedi, as will be seen 

 by a reference to the accompanying sections, and not as a vein, as is 

 sometimes stated by our chemical friends. There are plenty of 

 traces of former life in the bed : thus, I have obtained from it 

 numerous casts of Modiola, Aviciilojoeden, Orthoceras, Orthis, Lin- 

 gula, and fragments of Trilobites ; but the fossils are not well 

 preserved, their organic structure having apparently been destroyed 

 by chemical agency. We may then, I think, regard this Phosphate 

 bed as the remains of a Laminarian zone of sea life, just as the 

 wide stretching, ferruginous sandy fossiliferous layers, in the same 

 formation, with their fossils often broken and confusedly huddled 

 together, are the remains of the Littoral zone of the same period. 

 The bed, as far as it has already been explored, gives us an area of 

 four miles long, by about eighty yards in width, — this being the 

 depth to which it is worked at Cwmgwynnen, in the nearly vertical 

 strata, and at all the points hitherto examined it maintains much the 



