658 MISS E. M. R. WOOD ON THE [Nov. I906, 



and frequently weather to a bright yellow or orange tint. It is in 

 these brilliantly-coloured bands that graptolites are most commonly 

 found. 



Like the Dolgau Beds, the Talerddig Grits and Shales strike 

 40° to 50° east of north, and dip north-westward at angles varying 

 from 45° to 55°. As exposed in the Tarannon River, they are 

 capable of division into the following lithological bands : — 



Thickness in feet. 



1 1. 6th shale-band 175 



10. 5th grit-band 1 <,-. n 



9. 5th shale-band J ^ 1U 



8. 4th grit-band 35 



7. 4th shale-band 35 



6. 3rd grit-band 30 



5. 3rd shale-band | 



4. 2nd grit-band I 170 



3. 2nd shale-band J 



2. 1st grit-band 70 



1. 1st shale-band 325 



Total 1150 



Unfortunately, the section is not quite complete either in the bed of 

 the river or on the banks, and therefore the exact thickness and 

 character of some of the bands are somewhat uncertain. 



The uppermost member of this Talerddig Group is a shaly one, 

 and differs at first but little in lithological character from the 

 Dolgau Beds above, although the small greywacke-flags have be- 

 come more numerous and individually thicker, while the pale- green 

 colours© characteristic of the Dolgau Beds has given place gradually 

 to a light-grey tint. No trace of a fossil has yet been detected in 

 this band. 



This 0th shale-band is underlain by the 5th and highest grit- 

 band, the first grit of which is exposed in the bed of the river, below 

 the small waterfall south of Dolgau Farm. At first the grits are of 

 no great thickness, and are interbedded with numerous shales and 

 flags ; but, as we descend the sequence, they come on in full force 

 immediately to the south of a small stream on the left bank, and 

 give origin to small waterfalls in the bed of the main river. This 

 5th grit-band is the most important, both in collective thickness and 

 in the size of the individual beds of grit; and it always makes a 

 conspicuous feature along the hill-sides wherever it occurs. It 

 contains at least twelve beds of grit of 2 feet and upward in 

 thickness, and a few of from 4 to 6 feet (if we disregard thin 

 shale-partings). Prom one of the thin shale-bands between the 

 two highest beds of grit the following species of graptolites were 

 obtained : — 



Monograptus nudus (f. C). 

 Monograptus crenulatus (R). 

 Monograptus cf. dextrorsus, 

 Linnrs. (R). 



The 5th shale-band below is not well exposed, and its limits 

 cannot be accurately defined ; but the presence of softer shales, 



Monograptus griestonensis (C). 

 Monograptus suhconicus (C). 

 Monograptus priodon (f. C). 

 /raptus discus (f. C). 



