proceedings: geological society 173 



according to Knowlton is indistinguishable from that of the Fort Union 

 and is distinctly a Tertiary flora. It also contains remains of turtles 

 and dinosaurs, particularly of the genus Triceratops which is diagnostic 

 of the Lance formation and which has, at least until recently, been con- 

 sidered by vertebrate paleontologists to be a distinctively Cretaceous 

 form. The Cannonball member contains an invertebrate and verte- 

 brate fauna of over fort}' species very closely related to the marine 

 cretaceous fauna of the Fox Hills sandstone. 



The distinctively marine fossils of the Cannonball member were 

 found near Haley, N. D., by C. J. Hares, and on Cannonball River, 

 N. D., by E. R. Lloyd at about the same time in 1912. The member 

 is thicker and better exposed on Cannonball River and this was accord- 

 ingly selected as the type locality. The strata are practically flat lying, 

 but a comparison of altitudes instrumentally determined on lignite 

 beds in the Fort Union show a small but persistent dip to the north- 

 east and north. The Cannonball member has been traced and mapped 

 in a strip extending from near Mandan, North Dakota, to the eastern 

 part of Harding County, South Dakota, a distance of about 130 miles. 

 The marine fossils were found throughout the whole of this distance. 



The mechanics of granite intrusion in the Black Hills, South Dakota. 

 Sidney Paige. In the Black Hills schists and quartzites form the mat- 

 rix for invading granite masses. The schists suffered marked deforma- 

 tion in the vicinity of the intrusive masses, being thro\^^l into closely 

 appressed recumbent folds and receiving a second schistose structure. 

 Parallel with this new structure there has been lit-par-lit injection. The 

 quartzite broke into blocks which became separated by the advancing 

 magma. These features suggest that the conditions under which the 

 intrusion occurred involved the lateral distension of the invaded rocks 

 though this distension took place under a great load. There is no 

 evidence that the magma was able to dissolve fragments of the schist 

 upon a large scale, and it seems that such assimilation as maj' have 

 occurred was merely incidental to physical or mechanical features, and 

 not a primary process inducing or permitting the advance of the magraa. 

 Through injection and impregnation the composition and specific 

 gravity of the schist approaches that of the granite. The prime cause 

 of the advance of deep seated mag-matic material is probably to be sought 

 in movements incidental to adjustments toward isostatic equilibrium. 

 As sea bottoms sink there is a landward transfer of material, and con- 

 tinents rise. Where there are weak spots strong warps develop, lateral 

 distension results, and the upward invasion of the magma is permitted. 



Frank L. Hess, Secretary. 



