Crystallisation of Parisite. 557 



Wulfenite.— Thin coatings of light yellow color as well as 

 tiny crystals of wulfenite were found on smoky quartz in the 

 crocidolite pocket. The crystals are in part model-perfect 

 combinations of first-order pyramid with third-order prism 

 n (111), and,/ (320), (see fig. 6, p. 990, Dana, System), in part 

 cube-like combinations of a prism and the base. The amount 

 of wulfenite is very small, and its presence is easily accounted 

 for by the association, in the same l-egion of the pegmatite, of 

 molybdenite and galena. 



Boston and Cambridge, Mass., 

 February, 1911. 



Art. XL7VI. — Notes on the Absence of a Soil Bed at the 

 Base of the Pennsylvania^ of Southern Ohio;* by Jesse 

 E. Hyde. 



Bailev Willis has recently urged, as one of the fundamental 

 principles of paleogeography, the theorem that the failure of 

 repiesentation of many horizons and formations in an area 

 where sedimentation has otherwise apparently been continuous, 

 is to be explained by submarine erosion or failure of deposition 

 due to current action, and that it is unnecessary to assume 

 subaerial erosion in order to explain such a break in sequence.f 

 E. O. Ulrich has since seriously questioned the validity of the 

 grounds for Willis' stand, and his discussion with Willis' reply 

 are briefly abstracted in the minutes of two recent sessions of 

 the Geological Society of Washington.;}: Although these 

 remarks are not a formal presentation of either side, it is felt 

 that they open up to discussion one of the most important 

 points in paleogeography and one about which it is apparent 

 much remains to be learned. John M. Clarke's eloquent 

 appeal for more facts to support scientific theory, appearing in 

 the same number of Science with these abstracts, is as timely 

 to the present instance as to any of the unproved propositions. 



One of the principal arguments cited b} T Willis to support 

 this theorem is the absence of anything resembling a soil bed 

 or in any way suggesting weathering due to exposure to the 

 atmosphere at the plane which marks such an omission from 

 the column. It is maintained that if the bed whose absence 

 it is desired to explain had been eroded while the whole stood 



* By permission of the State Geologist of Ohio. 

 \ Science, N. S., vol. xxxi. pp. 241-260, 1910. 

 J Science, N. S., vol. xxxiii, pp. 312-316, 1911. 



