238 Reports & Proceedings — Edinburgh Geological Society. 



flexibility neutralized local weakness ; but with the adoption of 

 rigidity the problem reappeared. Hence arose " plate-complexity ". 



The formation of compound plates is discussed. "Grouping" 

 precedes, and is distinct from, combination. Plate-reduction is due 

 to "growth-pressure"; combination to tubercle-growth. Elaboration 

 of combination culminates in the Echinometridse, where the compounds 

 regain " Bothriocidaroid " proportions. 



In irregular Echinoids no combination occurs; grouping is often 

 developed. Secondary specialization in Spatangids produces 

 " Palaeozoic " structures. 



The Holectypoida show four ambulacral types : 



(1) Plesiechinid (triad-groups adorally, primaries adapically); 



(2) Pygasterid (primaries throughout); 



(3) Pyrinid (triad-groups throughout) ; 



(4) Discoidiid (triad-groups adorally, dyad-groups adapically). 

 Plesiechinid is primitive, and resembles the early Acrosaleniid 



type. Pygasterid indicates simplification, being morphogenically 

 transitional from Diademoid to Spatangid structure. Pyrinid is 

 persistent, resembling the "Echinoid" structure of Diademoids. 

 Discoidiid is exceedingly elaborate, showing extreme plate-reduction. 



The Cassiduloidea are divided into Nucleolitoida and Cassiduloida 

 (restr.). The former order is related, to the Pygasteridee ; its simpler 

 members have Plesiechinid ambulacra, and Holectypoid structures 

 appear in later forms. The Cassiduloida evolved through the 

 Echinoneidse. 



There are three main trends of evolution in Echinoid ambulacra : 

 (i) Diademoid, attaining plate-combination; (ii) Clypeastroid, 

 attaining plate-destruction ; and (iii) Spatangoid, reversionary. 



III. — Edinburgh Geological Society. 

 February 19, 1919. — Professor Jehu, President, in the Chair. 



1. " A Historical Sketch of the Iron Industry in Scotland." By 

 M. Macgregor, M.A., B.Sc, of H.M. Geological Survey. 



Mr. Macgregor sketched the rise and development of iron-working 

 in Scotland, more particularly in regard to the raw materials used. 

 The small primitive furnaces of early times known as Bloomeries 

 were described, and an account was given of the iron-works in 

 operation in the Loch Maree district during the first half of the 

 seventeenth century. The later furnaces in the central and west 

 Highlands during the eighteenth century were then noticed in some 

 detail. In all these charcoal was used as fuel. The smelting of 

 Scottish Carboniferous clayband ores by means of coke and coal came 

 into vogue soon after 1750, the year in which the Carron Ironworks 

 began their long career. Since that time there had been three main 

 stages in the development of the modern iron industry. These were 

 as follows: (1) Rise of the Clayband Industry, 1760-1830; (2) Rise 

 of the Blackband Industry, 1830-60 ; (3) Rise of the open-hearth 

 Steel Industry, and period of imported ores, 1850 onwards. 



2. Exhibition of Specimens of Norwegian Nepheline Syenite 

 (Laurdalite) Boulders from Flotta, Orkney. By Dr. J. S. Elett, E.R.S. 



