Rath^Neio Crystalline Form of Silica. 281 



tial to the formation of the Cotteswold valleys, and it is a fact that 

 there are fractures in many of the valleys ; but this is not enough, 

 the existence of the conditions needful for the action of tides along 

 lines of fracture must be shown ; — the land must have been low 

 enough for the tides to reach it, and the fractures must have been 

 opened into fissures wide enough to admit large volumes of water, 

 and long enough to account for the formation of the long valleys as 

 they now exist. There is no evidence of these things. 



A close connection exists between combes and springs ; there are 

 no combes without a spring, and when a combe forks there is a 

 spring in each branch. It may be said that the excavation of combes 

 by the sea would cause springs ; but in this case surely some of the 

 combes should be without springs, as one can hardly suppose that 

 the sea would make combes only where subterranean springs abounded. 

 This connection of combes and springs makes it hard to account for 

 the formation of the former except by means of the latter. 



The widening of the valleys is owing in great part to slips ; but 

 this process is now somewhat checked by the streams having been 

 made more or less artificial, and therefore hindered from carrying 

 away fallen matter. The slips from the Fuller's Earth are very 

 many ; there is hardly a combe cut into that formation and the over- 

 lying Great Oolite without a slip, sometimes stationary at present, 

 sometimes moving slowly ; indeed where Fuller's Earth occurs on an 

 escarpment a great part of the slope is moving. The Inferior Oolite 

 has so tumbled that it is not uncommon to find quarries of the Free- 

 stone on the sands below, or on the Upper Lias. 



The ^slopes facing south or south-west are more denuded and less 

 steep than others, because more exposed to rain. 



A very large amount of earth is carried away by springs and 

 storm-waters ; frost too has a great effect on soft Oolitic rocks. 



In going up a valley one finds that the volume of the stream gets 

 less, and so also does the amount of denudation, until the valley is a 

 mere hollow, and at last vanishes. Then, within a few yards, the 

 ground begins to slope in the opposite direction, and gradually takes 

 the form of a valley like the former, but falling the other way. 



Sub-angular gravels, which cannot be looked on as marine, but 

 only as subaerial and fluviatile, are found in the valleys at heights 

 ranging from 200 to 700 feet : it is clear therefore that like con- 

 ditions held during the whole period of the formation of the valleys, 

 and that no such deposits could have taken place in valleys washed 

 by tidal waters. — W. W. 



III. — Peeliminaby Notice of a New Crystalline Fokm of 



Silica. — By Professor G. von Path. 



[Poggendorff's Annalen Band CXXXIII.] 



THE two great groups of Silica, the crystalline (Quartz) and the 

 amorphous (Opal), with the respective densities of 2*65 and 

 2'2 — 2-3, appear likely to have a third and intermediate species 

 added, which, crystallising in forms belonging to the rhombohedral 



VOL. V. — NO. XLVII. 19 



