Notes on mineralogy. No. II. On the chemical composition of the granites of the south-east of Ireland / by Samuel Haughton.

  • Haughton, Samuel.
Date:
[1855]
Catalogue details

Licence: Public Domain Mark

Credit: Notes on mineralogy. No. II. On the chemical composition of the granites of the south-east of Ireland / by Samuel Haughton. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Such being the state of geological knowledge on this subject, it occurred to me that it might be useful to direct attention to a distinction of a chemical character which appears to exist between these two groups of gratiites,—a distinction to which I have been led in the course of a series of analyses of Irish granites, ni which I have been for some time engaged. The distinction to which I have alluded is the following. The granites of the main chain contain more potash than soda; and vice versa, the granites to the east of the chain, which are isolated from it and from each other, contain more soda than potash; showing that the circumstances, unknown to us, under which the isolated granites were formed, were such as to yield to the molten mass a quantity of soda greater than that possessed by the granites of the principl chain. In illustration of the foregoing generalization, I offer analyses of granites from the following localities :— 4. 5. 6. 7. 8. Granitic chain. Dalkey, Co. Dublin. Foxrock, Co. Dublin. Three Rock Mountain, Co. Dublin. Enniskerry, Co. Wicklow. Ballyknocken, Co. Wicklow. Killljallyhugh, Co. Cai-low. Blackstairs, Co. Wexford. Ballyleigh, Co. Vv'^exford. Isolated granites. 1. Cushbawn, Co. Wicklow. 2. Crogban Kinshela.Co.Wicklow. 3. Ballymotymore, Co. Wexford. 4. Ballvnamuddagh, Co. Wexford. It will be seen, on reference to the Ordnance Ma]), or any good map of Ireland, that the localities selected extend from the north to the south of both the granite scries; and on reference to the geological maps of Wicklow and Wexford, it may be ob- served by those unacquainted with the geological structure of this part of Ireland, that the granites of the second group ex- amined are taken from the distinct and distant isolated patches of granite. In order to investigate the relative proportions of quartz, fel- spar and mica, of which these granites were composed, I used the following method, which appears to be as simple as any that has been proposed for such a purpose. Let the per-centage of silica in the granite be divided by the atomic weight of silica, and let the quotient be denoted by a. Let the per-centages of alumina and peroxide of iron be divided by the atomic weights of alumina and peroxide of iron respect- ively, and let the sum of the quotients so found be denoted by b. Let the per-centages of lime, magnesia, potash, and soda be divided by the atomic weights of these elements, and the sum of the quotients called c.