Reports & Proceedings — Edinhurgli Geological Society. 93 



relationship of the gypsum to the beds of anhydrite with which it is 

 sometimes associated. 



A description is given of a remarkable breccia occurring at 

 Chellaston in Derbyshire, and its origin is discussed. Important 

 occurrences of gypsum in other parts of the countiy, as well as the 

 alternative theories as to their mode of formation, are then reviewed 

 in the light thus obtained. 



The remainder of the paper deals mainly with the possible 

 interchanges between anhydrite and gypsum. The place and 

 the function of the fibrous form of gypsum are indicated, and 

 a nomenclature is suggested for certain isolated masses of the 

 mineral. 



The chief conclusions are as follows : — 



1. At Chellaston the gj^psum was laid down as such, and has 

 suffered no appreciable alteration or addition since the time of its 

 original deposition and brecciation. There is no evidence that the 

 rock was ever anhydrous. 



2. By comparison with this deposit, and also by independent 

 evidence, it seems probable that most of the important beds of 

 gypsum in the country were laid down as gypsum, and have behaved 

 throughout as stratified deposits. 



3. When anhydi'ite is present, the evidence favours the view that 

 it is original, and was deposited in a stratiform manner in sequence 

 with gypsum. 



4. Microscopic evidence shows that there has been, in some cases, 

 an alteration of anhj^drite into gypsum where the two minerals were 

 in original juxtaposition ; this alteration, however, is considered to 

 have occurred at, or iinmediateh^ after, the time of deposition, and 

 to be confined to the existing plane of contact of the two minerals. 



II. — Edinbuegh Geological Society. 

 Decemler 19, 1917. — Professor Jehu, President, in the Chair. 



1. "Marginal Intrusive Plienomena near Linlithgow and at 

 Auchinoon." By T. Cuthbert Day, F.C.S., F.K.S.E. (Illustrated 

 by lantern views and rock specimens.) 



At Hillhouse Quarry, near Linlithgow, the dyke of white trap 

 with its branches has produced considerable contact alteration in the 

 limestones and shales, while the thick sheet of columnar olivine 

 basalt which overlies the sediments does not appear to have caused 

 any change ; it, however, transgresses the strata considerably, 

 which, it is suggested, may be due to contemporaneous erosion and 

 that the basalt may prove to be a lava. 



It was pointed out that the peculiar brecciation seen in certain 

 bands of dolerite at Cockelrue which have been enclosed in the 

 intrusive mass of the hill is probably due, not to crushing or move- 

 ment, but to numerous crack joints produced on cooling. 



The dolerites of the district do not readily take the form of white 

 trap when found in contact with carbonaceous shales. 



A large exposure of intrusion breccia was described in a quarry of 



