J. ParJi'uisoii — The Maldng of Quart::, Schist. 259 



usually less than half their diameter apart, in some cases almost 

 contiguous ; margin slightly exsert, but calyx sunk below general 

 surface ; walls crenulated and infolded to form twelve short septa, 

 extending inwards from one-quarter to one-third the diameter of 

 the calyx. Smaller corallites (coenenchyma) not numerous, usually 

 only 2-4 irregular rows between the larger corallites ; polygonal 

 in shape, with well-developed walls and regular horizontal and 

 mostly equidistant tabulae, so as to divide the tubes into a series of 

 square cells. 



MiSASURBBIENTS. mm. 



Diameter of calyx of larger corallite ... ... ... 1-1-5 



Length of coralium .. . .. ... 80*0 



Diameter of corallum at base 20"0 



Diameter of corallum at crown ... ... ... ... 55-0 



Remarks. — This species differs from H. Grayi^ in the rounded or 

 lobate form of the branches, and in the number, approximation, and 

 depression of the calices of the larger corallites. From H. inordinata 

 it diifers by possessing stouter, more lobate branches, more numerous, 

 closer and larger corallites with depressed calices, and less abundant 

 coenenchyma. A Norwegian species named Plasmopora ramosa, Kiar, 

 has been recently described - which bears a considerable resemblance 

 to H. ccespitosa, and is stated to be closely allied to IT. Grayi. It 

 differs in the more exsert margins of the corallites, the absence of 

 septal prominences, and in the wider spaces between the corallites. 

 The internal structure, moreover, which is the most important 

 feature, appears to be distinct. 



EXPLAJSTATIOJSr OF PLATE XVI. 

 Figs. 1, 2. — Goniophora ffrandis, Salter. "Wenlock Limestone : Dudley. Fletcher 



Coll. jSTat. size. 

 Fig, 3. — Modiolopsis mimiis, Salter. Upper Ludlow: Lesmahagow. Enlarged 



X nat. size. 

 Figs. 4, 5, — Orthonota SugJiesi, Salter. Lower Llandovery Beds (Upper Bala, 



Salter) : Sefiu Llettyrhyddod, Llandovery. Fig. 4, side view ; Fig. 5, 



hinge aspect of .shell. Enlarged lA- nat. size. 

 Fig. 6. — Hcliolitcs caspitosa, Salter. Wenlock Limestone: Dudley. Fletcher Coll. 

 Fig. 7. — Portion of corallum, enlarged f nat. size. 



Ill, — On the Making of a Quartz Schist. 

 By John Pakkinson, F.G.S. 



IN a paper published^ some eight years ago, Prof. T. G-. Bonney 

 discriminated between the dominant characteristics of quartz 

 schists from the Alps and quartzites modified by pressure. The 

 distinctions as therein pointed out may be thus summed up. 



In a quartz schist we find an absence of indications of original 

 fragments, the shape of the quartzes proving that they were formed 

 in situ ; together with no evidence " that the mica in its present 

 form is derivative"; from which it almost necessarily follows that 



1 Edwards & Haime : Brit. Foss. Corals (Palseont. Soc), p. 252, pi. Iviii, fig. 1. 



' Eaar: Die Korallenfaun, Et. 5, Norweg. Silur., p. 32, t. v, figs. 5-6: 

 PalcTontographica, Bd. xlvii, 1899-1900. 



» Geol. Mag., Dec. Ill, Vol. X (1893), p. 204 ; also Geol. Mag., Dec. IV, 

 Vol. Ill (1896), p. 400 (" On a Pebbly Quartz-Schist from the Val d'Anniviers"). 



