Salter — On the May Hill Sandstone. 201 



sometimes, as in E. Altensteinii, a quarter of its diameter composed 

 of the persistent bases of the petioles. This also is a character as 

 we have seen of the genus Cycadoidea, and our species may be dis- 

 tinguished from the others by the regiilar arrangement and symmetri- 

 cal form of the bases of the petioles. They are rhomboids, the horizontal 

 diameter of which is but little more than the perpendicular, and differ- 

 ing in this respect not only from all the other described recent species, 

 but also from all the living Cycads with which I am acquainted. 



EXPLANATION OF PLATE IX. 



Cycadoidea Tatesii, Mor. and Car. From the specimen belongino^ to tlie Museum of 

 the Eoyal Agricultural College at Cirencester. Two thirds the natural size. 



Fig. 1. a. The persistent bases of the petioles, b and c. The lower portion of the 

 stem, deprived of its outer covering, and showing at c the thin external 

 layer of cellular tissue, and at b the outer surface of the woody cylinder. 



Fig. 2. The upper surface of the same stem. a. The internal cavity occupied by the 

 pith, but in the specimen figured containing amorphous iron-ore. b. The 

 inner woody ring. c. The outer woody ring, d. The bases of the 

 petioles. 



I 



m. — On the May Hill Sandstone. 

 By J. W. Salter, A.L.S., F.G.S. 



T is at all times difficult to fix the parentage of a new geological 

 idea. So many circumstances and so many hints and observations 

 converge to its establishment, when the due time comes for its appre- 

 ciation, that, looking back, it seems hardly possible to disentangle 

 the ideas of one workman in science from the suggestions of another. 

 Hence it is always difficult to establish an exact priority of claim in 

 questions which have remained long unsettled. 



In the elaborate, but too short volume by Prof. Eamsay and my- 

 self, on the Geology of North Wales (Mem, Geol. Surv. vol. iii. 

 1866), an attempt is made by the former to give a succinct history 

 of the order of discovery of the various members of the British 

 Silurian (and Cambrian) groups. With respect to the May Hill 

 Sandstone — a group most important, as all will now recognize, as 

 the key to the structure of Wales and the bordering Silurian coun- 

 ties, — I will add a few facts which suggest themselves to me on 

 reading Prof. Eamsay's brief and important chapter on the nomen- 

 clature (chap. i.). 



Even before the publication of Prof. Phillips' memoir on the 

 Malvern Hills, 184:8, it was observed by the Professor, then paleon- 

 tologist to the Survey, that the Caradoc and May Hill Sandstone of 

 the Silurian System included an upper group, distinguished by 

 the prevalence of Upper Silurian fossils ; and this upper rock of the 

 Malverns was distinguished by the teim, "Upper Caradoc," — a bad 

 name, since Sir E. I. Murchison had already called it May Hill Sand- 

 stone. It was known in 1848, by the Survey, that this Upper Cara- 

 doc ranged unconformably round the great Cambrian and Lower 

 Silurian Island (so to speak) of the Longmynd, resting at one place 

 on Llandeilo rocks, at another on the still older slates of the Long- 



