258 



W. J. SOLLAS ON A NEW LYSSAKINE HEXACTINELLID 



possibly owing to its being incomplete and yet simulating complete- 

 ness through a sharpening of its ends by solution. The axial canal 

 can be clearly traced through one half of it only, the other half being 

 rendered opaque by the close firm network of cavities which exca- 

 vate it. 



Leaving out of consideration the last, which is a doubtful form, 

 and a few other fragments not figured and quite undeterminable, one 

 may safely say that all the spicules extracted from the small 

 fragment of dolomitic chert are distinctly Hexactinellid ; and it 

 would appear that we probably have here, not a heterogeneous mix- 

 ture of spicules derived from several kinds of sponge, as is usually the 

 case in chalk-flints, but the much rarer case of a natural assem- 

 blage of forms derived from a single individual. For this group of 

 forms we propose a distinct name, Astroconia Granti, the. specific 

 designation being given in honour of the indefatigable observer to 

 whom we are indebted for our knowledge of the sponge. 



The Quartz Crystals. — These do not differ in character from those 

 described from the Carboniferous Limestone by Mr. Wardle and in 

 my papers on Catagma (Ann. & Mag. Wat. Hist. ser. 5, vol. ii. p. 361, 

 fig. 3), and on Mints (vol. vi. p. 445). I have also called attention to 

 the important part which such such crystals play in rock-formation 

 by pointing out that certain beds of sandstone in the Eden valley 

 appear to partly consist of them. If we knew the bulk of these beds, 

 we might calculate the amount of limestone which must have been 

 denuded to produce them, on the assumption that this limestone con- 

 tained 1 oz. of crystals in every 10 lb. of rock, as is the case with 

 that at Buxton at the present day. I believe that in these quartz 

 crystals, derived undoubtedly from siliceous organisms, we have also 

 the key to the origin of the " krystallinische Quarzpsammite " of 

 Kallmann, which occur in several formations on the continent (Zir- 

 kel, Lehrbuch der Petrologie, vol. ii. p. 575). They are nothing 

 but the insoluble residues of limestone masses which have been 

 dissolved away by the action of subaerial waters *. If this be so, 

 we have in these crystalline sandstones the last stage of one of those 

 beautiful cycles or, rather, spirals which appear to characterize the 

 operations of nature : the silica derived from the disintegration of igne- 

 ous rocks is carried in solution into the ocean and there built up by 

 living organisms into forms of endless diversity and exquisite beauty ; 

 this organic silica again yields to solvent influences and afterwards 

 crystallizes out amidst calcareous sediments in perfectly formed 

 crystals of mineral quartz ; the calcareous rocks elevated above the 

 sea-level are exposed to water and the weather ; solution proceeds 

 apace ; and after the carbonate of lime has become dissolved away, the 



* This statement is too absolute. The beautiful observations of Mr. J. A. 

 Phillips, F.Gr.S., in complete accordance with those of Prof. Bonney and 

 Dr. Sorby, show that crystalline quartz-sandstones are sometimes formed in a 

 quite different manner — indeed, that the formation of quartz crystals has been 

 subsequent to that of the sandstone as a whole. In deciding upon the origin of 

 such sandstones, we shall have probably to be guided by the circumstances in 

 each case, before we can say certainly that the constituent quartz crystals are 

 original or superinduced formations. 



