ENDOLITHIC BRECCIATION 537 



containing anhydrite, which by hydration is changed to gypsum. 

 This process involves an increase in volume, estimated by some 

 (Credner, Fritsch, Bauer, Geikie) as low as 33 per cent., and by 

 others (Naumann, Zirkel, J. D. Dana) as high as 60 per cent. 

 J. Roth, indeed, has calculated that the increase in volume resulting 

 when anhydrite takes up two molecules of water of crystallization 

 to form gypsum is as high as 62.3 per cent. 



It is probably true that calcium sulphate is largely deposited in 

 the anhydrous statr^, especially when it originates under arid condi- 

 tions (see ante, Chapter IX). Certain it is that anhydrite abounds 

 in many of the older strata along with gypsum, and it is not im- 

 probable that in such cases the gypsum is the result of hydration of 

 the anhydrite. In view of the great force exerted within the rock 

 mass by the expansion due to this hydration, we would expect to 

 find the results in a shattering and deformation of the enclosing 

 strata. This expectation is commonly realized, for such endolithic 

 brecciation is a frequent if not constant accompaniment of gypsum- 

 bearing strata, especially in the Palseozoic. Cases have been de- 

 scribed from the Salina and Monroe beds of New York, Ohio, 

 Michigan, and Canada. (Grabau and Sherzer-i i :i>o ; Kraus- 

 18 i/d/-///.) Brecciation of this type is not uncommon in salt 

 deposits, where through recrystallization a pronounced pressure 

 results, which may even affect the enclosing strata, deforming and 

 disrupting them. This subject will be more fully discussed in the 

 chapter on diagenism. 



BIBLIOGRAPHY XII. 



1. BROWN, THOMAS C. 19 13. Notes on the Origin of Certain Pateozoic 



Sediments, Illustrated by the Cambrian and Ordovician Rocks of Center 

 County, Pennsylvania. Journal of Geology, Vol XXI, pp. 232-250. 



2. COLEMAN, A. P. 1907. A Lower Huronian Ice Age. American Journal 



of vScience, 4th series, Vol. XXHI, pp. 187-192. 



3. COLEMAN, A. P. 1908. Ancient Ice Ages and Their Bearing on Astro- 



nomical Theories. Journal of the Astronomical Society of Canada, Vol. 

 II, No. 3, pp. 132-135- 



4. COLEMAN, A. P. 1908. The Lower Huronian Ice Age. Journal of 



Geology, Vol. XVI, pp. 149-158. 



5. COLEMAN, A. P. 1908. Glacial Periods and Their Bearing on Geological 



Theories. Bulletin of the Geological Society of America, Vol. XIX, pp. 

 347-366. 



6. CROSBY, WILLIAM OTIS. 1891. Composirion of Till or Boulder 



Clay. Boston Society of Natural History Proceedings, Vol. XXV, pp. 

 1 15-140. 



7. CROSBY, W.O. 1896. Englacial Drift. American Geologist, Vol. XVII, 



pp. 203-234. 



