II.—On Analysis of White Chalk from the County of Tyrone, with Note on the Occurrence of Zinc therein, and in the overlying Basalt

• Published in: Geological Magazine
• Main Author: Hardman, Edward T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1873
• Subjects: Geology; Carbonic acid
• Online Access: http://dx.doi.org/10.1017/s0016756800466586; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800466586

I was led to make this analysis with the view of determining if possible whether the extreme hardness of the Irish Chalk were due to either a chemical, a mechanical, or a calorific alteration, from the influence of the overlying basalt. If it were owing to chemical change, we should expect to find a large per-centage of silicates and a diminution in the amount of lime; if to the influence of heat, carbonic acid would be driven off, silica would be in excess, and the presence of the insoluble bases, such as the peroxide of iron, oxide of manganese, and alumina, would become more apparent; while if a mechanical cause or pressure were the reason, no change would take place in the relative amount of the constituents. I believe the result seems to show that the induration of the Chalk must be set down chiefly to the last agency,—if to anything apart from the original formation of the rock,—and that the power of alteration exerted over it by the heat of the molten basalt has been small indeed. At the same time a certain addition has been made to it by means of water holding chemical bodies in solution.