152 The Ottawa Naturalist. 



8. Resume of General Stratigraphit Relations in the Atlantic Coastal Plain from 

 New Jersey to South Carolina. By Air. N. H. Darton, Washington, D. C. 



o. Cretaceous Plants fiom Martha's Vineyard. Results Obtained from an Exam- 

 ination of the Material Collected by David li'hi/e in iSSg. By Mi. Arthur 

 Hollick, New Brighton, N. V. 



10. On Asbestos ami Asbestiform Minerals. By Dr. George P. Merrill, Washing- 

 ton, D. C. 



The paper treats of the composition, mode of occurrence and mituralogical 

 nature of the various minerals commercially grouped under the name of asbestos, 

 and attempts to explain their fibrous structure as due to abnormal elongation of the 

 mineral parallel to the vertical axis, the individual fibres being in part at least 

 by prismatic faces, that is by the planes of easiest cleavage. The primary cause of 

 this elongation is believed to be mainly dynamical, a result of shearing and other 

 earth movements such as are productive of uraltic hornblendes, schistosity or even 

 slaty structure and slickensided surfaces, where actual fiacturing takes place. 



//. Pre-Cambrian Volcanoes in Southern Wisconsin. By Prof. Wm. H. Hobbs, 

 Madison, Wis. 



A preliminary report on the study of a group of isolated areas of igneous rocks 

 which protrude through the Potsdam sandstone in the valley of the Fox River, Wis- 

 consin. Some of these areas represent local outflows of rhyolitic lava winch exhibits 

 superb examples of spherulitic, peritic, fluxion, and breccia structures. The origin- 

 ally glassy ground mass of these rocks has become devitriried hence they are apo- 

 rhyolites, and they have been subjected to dynamic metarr.orphism and subsequent 

 infiltration of silica. They are intruded by dikes of both basic and acid rocks. 

 Specimens and photographic sections were exhibited. 



12. A Geological Sketch of the Siena Tlayacac, in the State oj Morelos, Mexiio. 

 By Paof. A. Capen Gill, Ithaca, N. Y. 



/j. Syenite-Gneiss (Leopa-d Rock) from the Apatite Region of Ottawa County, 

 Canada. By C. H. Gordon, Beloit, Wisconsin. 



The rock here described appeared in the exhibit of the Canadian Geological 

 Survey, at the World's Fair under the title of " Concretionary Veinstone," from the 

 apatite region. It consists of irregular ellipsoidal or ovoid masses of feldspar, with 

 more or less quartz, separated by narrow, anastomosing bands of interstitial material 

 consisting chiefly of green pyroxene. The ellipsoidal masses are of all sizes up to two or 

 three inches in cross section, and several inches Ion?. The field study at High Kock 

 Mine, Ottawa County, shows this rock to occur in dikes intersecting the pyroxenites 

 and quartzites. In some places the rock is very coarse with no indications of the 

 ellipsoidal structure, while in others it is a distinctly banded gneiss whose identity 

 with the ellipsoidal rock is evident from the anastomosing of the augite bands on a 

 cross fracture face. Ordinarily the rock has very little quartz and corresponds to a 

 pyroxene-syenite, but in some places the quartz is much more abundant thus allying 

 it to the pyroxene-granites. In view of its gneissic structure and usually sparing 

 amount of quartz the rock is here referred to generally as syenite-gneiss, though 

 grading locally into forms which may more fittingly be regarded as granite-gneiss. 



The presence of a distinct gneissic microstruclurc, taken in connection with 

 other lacts appears to establish the conclusion that the peculiar ellipsoidial structure is 

 due to orographic forces acting upon a coarsely crystallized rock in which principal 

 constituents (feldspar and pyroxene) are more or less irregularly distributed. The 

 breaking ol the rock undei pressure has been attended by the recrystallization of the 



