446 MISS B. M. E. WOOD OK THE LOWER LTJDLOW [May 1 9OO, 



(1) The Dee Valley. — My friend and colleague Miss Elles, who 

 visited this district in 1899, has kindly placed her notes and speci- 

 mens in my hands. She recognized two well-marked graptolite- 

 zenes in the Nantglyn Flags, which Mr. P. Lake correlates with ihe 

 Lower Ludlow Shales, while the zone of Monograptus leintwanlin- 

 ensis (typical form) occurs at a considerably higher horizon. The 

 succession is as follows : — 



(3) Zone of Monograptus leintwardinenszs. 

 (2) Upper Gritty Beds, unfossiliferous. 

 (1) Nanfglyn Flags. 



(b) Zone of Monograptus Nilssoni. 



(a) Zone of Monograptus vulgaris. 



M. vulgaris occurs in various exposures south of ISTant Arddan, 

 while M. bohemieus and M. Nilssoni are seen in abundance in the 

 gritty bands exposed in the Deeside slate-quarries. The rocks are 

 for the most part too cleaved to make it possible to determine what 

 form of M. colonus it is that occurs in association with M. bohemieus 

 and M. Nilssoni in this zone. It is interesting to find that 

 M. hintwardwensis here is the typical form of this species ; I have 

 examined specimens from the Llantisilio Road and from Pen-y-Vivod. 



(2) The Lake "District. — Mr. Marrhas kindly permitted me to 

 examine the specimens of Wenlock and Ludlow graptolites collected 

 by himself from the Lake District. At the time when his paper 

 ' On the Wenlock & Ludlow Strata of the Lake District' 1 was 

 published, Barrande's type-forms were uncertain and the Upper 

 Wenlock and Lower Ludlow Beds of the West of England had not 

 been zonally separated, nor had their graptolite-species been clearly 

 defined. Judging from the results now obtained, I should be 

 inclined to group the Ludlow Beds of the Lake District as 

 follows : — 



I 5. Bannisdale Slates. Zone of M. leintwardinensis var. incipiens. 



Lower Ludlow j |' Uppel°Ooldwell Beds. } Zone ° f Mono P' a P tus Nilssoni. 



[2. Middle Cold well Beds. ?Zone of Monograptus vulgaris. 

 Upper Wenlock 1. Lower Coldwell Beds. Zone of Monograptus Ni/ssoni= 



? Cgrtograptus Carruthersi. 



. The Middle Coldwell Beds have not hitherto yielded graptolites, 

 and therefore their exact horizon is uncertain. They may possibly 

 represent the zone of M. vulgaris, or that species may eventually 

 be detected in the lower part of the Upper Coldwell Beds. The 

 examples of M. colonus collected from the Upper Coldwell Beds and 

 Coniston Grits agree more closely than any other British examples 

 known to me with Barrande's most typical form. The specimens of 

 M. leintwardinensis from the Bannisdale Slates belong to the variety 

 which I call incipiens, and its horizon is the same here as in the 

 Long Mountain district. 



1 Geol. Mag. 1892, pp. 534 et seqq. 



