714 



SCIENCE. 



[N. S. Vol. III. No. 71. 



Since the sprouting from the stump of coni- 

 fers, especially pines, is most unusual and at least 

 the persistence of the sprouts has generally been 

 doubted, this exhibit under the specially un- 

 favorable conditions cited is of great interest. 



The well-observed capacity of the species to 

 develop adventitious buds seems here to serve 

 for the purpose of maintaining the occupancy of 

 the soil. Cones develop on 3 to 5-years-old 

 sprouts, but germinative seeds are rarely found. 

 F. A. Lucas, 



Secretary. 



GEOLOGICAL SOCIETY OF WASHINGTON. 



At the 43d meeting, held in Washington, D. 

 C, April 22, 1896, communications were pre- 

 sented as follows : ' A new Laccolite Locality 

 in Colorado and Its Rocks,' by Mr. G. K. Gilbert 

 and Mr. Whitman Cross ; ' The Origin of some 

 Mountain Scarps, ' by Mr. M. R. Campbell. 



Mr. Gilbert described a laccolitic locality dis- 

 covered last summer in southern Colorado. Da- 

 kota and older rocks are bent into a dome with 

 a height of 1,000 feet and a width of 5 miles. 

 Many dikes traverse this and two laccolites are 

 exposed in partial section. The horizons of 

 intrusion are more than 600 feet below the base 

 of the Dakota. The date of intrusion is approx- 

 imately indicated as Eocene or late Cretaceous. 

 The intruded rock is more basic than is ordi- 

 narily found in laccolites and is much more 

 easily disintegrated by weathering. The neigh- 

 boring sandstones and those portions of neighbor- 

 ing shales which have been baked by the intru- 

 sions resist erosion better than the igneous rocks, 

 so that the laccolites find topographic expres- 

 sion in valleys instead of hills. A mass of al- 

 tered sandstone, protecting a pedestal of shale 

 and igneous rock, stands prominent above the 

 country, constituting the crest of Twin Butte, 

 the most conspicuous landmark of the region. 



The rocks of the laccolite and dikes were 

 described by Mr. Whitman Cross. The rock of 

 the laccolite and of most of the dikes is a basic 

 syenite porphyry, in which the ferromagnesian 

 silicates, augite, biotite and olivine, exceed 

 the feldspathic constituent. Augite is the pre- 

 dominant silicate. These rocks are allied to 

 a large series from the plains of Coloi-ado 

 and New Mexico, to be described hereafter. 



Mr. M. R. Campbell discussed the origin 

 of the eastward facing scarp of the Blue Ridge 

 throughout North Carolina, which has been 

 attributed (1) to the action of sea waves on an 

 elevated coast, (2) to the normal erosion of a 

 broadly uplifted peneplain, and (3) to deforma- 

 tion produced by radial movements in the 

 crust of the earth. The first and second theo- 

 ries he regarded as obsolete or insufficient. 

 The third theory seems to offer the best expla- 

 nation, but deformation alone could hardly 

 produce the present scarp; there seems to have 

 been modifj'ing conditions which have not 

 heretofore been formulated, but which were 

 probably the immediate cause of the scarp pro- 

 duction. 



No radial mbvement is known to have oc- 

 curred in the Appalachians of sufficient inten- 

 sity to produce so steep a scarp, but if, during 

 a period of baseleveling, a slow monoclinal up- 

 lift occurs, the portion of the region which is 

 beyond the influence of the uplift will remain 

 at baselevel, whereas in that portion in which 

 the movement is at a maximum the process of 

 baseleveling will be interrupted producing a 

 very different succession of topographic forms. 

 There will be an intermediate zone in which the 

 forces of elevation and degradation will be 

 balanced against each other. 



If the movement is relatively rapid the pene- 

 plain will encroach but slightly upon the uplift. 

 If the movement is slow the peneplain will en- 

 croach to a much greater extent not only along 

 the streams, but in the inter-stream areas also. 

 The result of this encroachment is to accentuate 

 the slope produced by the uplift, and if the 

 movement is extremely slow the slope will be- 

 come a scarp. 



If this hypothesis is correct the peneplain 

 which caps the Blue Ridge is continu^ous with 

 the Piedmont plain at a very short distance 

 from the foot of the ridge, but the intermediate, 

 or sloping, portion of the old peneplain is almost 

 completelj^ removed by more recent erosion 

 along the zone of tilting. 



In the vicinity of Roanoke, Va., this uplift 

 turned toward the north and crossed the Appa- 

 lachian valley. In this portion of its course 

 similar -results were produced, but the rocks 

 are not hard enough to preserve the scarp as 



