228 RECORD OF SCIENCE FOR 1886. 



112. Dale, in a paper on the metaiuori)hisiii*iii the Kliode Island coal 

 basin, describes an area north of that previously stndied, in which the 

 beds are greatly disturbed and the alteration intense. The slates and 

 clays are found changed to mica schists, holding garnet, staurolite, 

 etc., and separated from equally ciystalline beds, at least in part of 

 Paleozoic age, by plumbaginous argillite, with veins of mica and coal 

 ferns.* 



113. KaoUnizaiion. — Lesley, in a paper on the kaolin of southeastern 

 Pennsylvania, discusses kaolinizution, and suggests that this process 

 and the resulting rock decay may be greatly increased by the presence 

 of limestone. It is thought that this would account for some of the 

 features observed in the district studied and in various belts of spe- 

 cially decayed rocks ; for instance, on the eastern side of Iloosac Mount- 

 ain and in parts of the Southern States, t The relation of decay to 

 joint planes is also considered, and Ashburner,| in an examination of a 

 kaolin deposit in Delaware County, hnds evidence confirming Lesley's 

 views. 



114. On the origin of coal. — Lesquereux, in a very interesting and sug- 

 gestive paper on this subject, urges the peat-bog theory with a great 

 mass of evidence from his own observations in the European peat bogs 

 and the coal measures of the United States. § 



TOPOGRAPHIC FEATURES OF LAKE SHORES. 



115. In a paper on this subject Gilbert discusses the several agents con- 

 cerned in the formation of the shores of water bodies in which tidal 

 action was insignificant in its results. The studies leading to the memoir 

 were in large part upon the topographic features of the lacustral de- 

 posits of the great fossil lakes of the Great Basin, and supplemental 

 observations have been made on the shores of some existing lakes. 

 Omitting considerations of tidal action, the agents concerned in the 

 production of shore features are waves and currents created by the 

 wind. The wind which drives waves toward a shore i^roduces also a 

 system of currents — superficial currents toward the shore and along the 

 shore, and an inferior current, the undertow, away from the shore. 

 The waves erode, and the waves and shore current in combination 

 transport the eroded material, shore drift, in the direction of the shore 

 current. Under certain clearly indicated conditions the shore drift is 

 deposited, its accumulation taking the form of spits, bars, hooks, etc. 

 In the region of erosion the laud is planed away just below the water 

 surface, and this planed surface in the fossil condition becomes a ter- 

 race. The shoreward limit of erosive action is marked by a cliff. In 



* Canadian Inst. Proc, vol. 22, pp. 18-21. 



t Second Geological Survey of Pennsylvania, Annual Report lor 1885, pp r)71-691. 



tibid., pp. 593-614. 



§ Ibid., pp. 95-124. 



