494 



THE GEOLOGIST. 



mineral crystallizing in veins according to the temperatures and precedence due 

 to eacli ; thus quartz crystallizes first, afterwards those the affinities of wliicli 

 bind them most strongly together, and which require longer time and lesser 

 temperature for becoming solidified. Veins running north and south, and veins 

 running east and w^est, often containing different deposits, may be accounted 

 for by currents having overlaid each other, and made saturations of distinct 

 kinds in any given spot ; and this draws me to say that were the former forces 

 and sources of the currents calculated, a perfect conclusion might be arrived at 

 respecting the shape of the present continents ; for no doubt the waters have 

 deposited and shaped the lands. At first, when no land broke the surface of 

 the globular sea, variation of temperature was the only source of its disturbance 

 besides the tides and the motions of our planet around its ads, so that those 

 acquainted with the laws of the winds and tides migiit readily surmise which 

 had been the point where the greatest accumulation of solid matter took place 

 in the shape of a reef or shoal, and how its first appearance above the level of 

 the sea affected the then state of things. In contradistinction to received 

 opinion, I should say the New World was the first formed, its unbroken coast- 

 line showing that the ciUTcnts were not then so complicated as they are now ; 

 but if you wiU give me an opinion on the subject, however crude the idea may 

 appear, it may help to elicit facts hitherto unt'hought of.— Your obliged corres- 

 pondent, A., Belfast. 



P.S. According to my theory, of course we must look on granite as having 

 been made from sand and sand from granite, the bosses into which it becomes 

 weathered shov/ing the seams of its deposit plainly enough. The sands of 

 Africa and of the other desert countries may lie on granite, the upper part of 

 which is still sand unchanged by igneous agency. 



Phosphate op Lime Nodules.^ — Dear Sie,— In reply to Mr. Mortimer's 

 letter addressed to you in Number 22 of the "Geologist," I am afraid I 

 cannot answer either of his questions satisfactorily ; for I am unable to say how 

 the phosphate of lime was detected in the nodules of the Upper Green Sand at 

 Cambridge in the first instance, although, as you justly remark, they have 

 long been known to contain it. Some of the nodules are supposed to be copro- 

 lites, from their peculiar form, and occasionally having scales and other remains 

 of fish, &c., embedded in them ; but the majority are, I think, not considered 

 to be organic, although they yield phosphate of lime ; for I believe it is now 

 acknowledged that this mineral occurs in rocks more extensively than was ima- 

 gined, without being derived from bones. When I w^as at the University, now 

 more than twenty years ago, these concretions were known to yield this phos- 

 phate ; but it is only of late years that the green sand has been so extensively 

 worked for economical purposes. I have not seen the preparation of the 

 nodules for agricidtural uses, but I beheve they are ground down in a miU, and 

 in due course, when properly prepared, may be applied as a manure in the same 

 way as guano, lime, and bone-dust. I have not written any special paper on 

 this subject, but m a lecture delivered last January, at the whiter meeting of 

 the Warmckshu-e Naturalists' Pield-Club, held at the Warwick Museum, on 



The History of Tossil Bone -beds," I suggested the possibility of the applica- 

 tion of the weU-known Lias " bone-bed" to this end, and I referred to the value 

 and importance of the green sand at Cambridge, and of the Crag m Suffolk, 

 from which such large quantities of phosphate of lime are now obtained. 

 I heard that a notice of this appeared in the Mark Latie Tlxpress, where it is 

 possible Mr. Mortimer may have seen it.— Paithfully yours, P. B. Brodie, 

 Vicarage, Rowmgton. 



PossiL Horns from Blue Clay, near Gatehouse.— There was lately found 

 ni the canal leading from the Bay of Pleet to Gatehouse a pair of horns attached 

 to a portion of tlie skull apparently belonging to an animal of the stag species. 



