946 



SCIENCE 



[N. S. Vol. XXIX. No. 754 



middle Cambrian fauna, and there is a non-fossil- 

 iferous group of quartzites, schists and hornfels, 

 which may be of any age from lower Cambrian to 

 Ordovician. The Carboniferous sediments com- 

 prise the so-called Koxbury conglomerate and 

 Cambridge slate. 



About forty varieties of igneous rocks are sepa- 

 rated into the following groups on the basis of 

 consanguinity, association and structural rela- 

 tions : ( 1 ) a " gabbroic " group, including gabbro, 

 basalt, diorite, amphibolite, etc., of presumably 

 Oraovician age, and represented in the diorite 

 complex of Swampscott, etc.; (2) a "tonalitic" 

 group, comprising granite, tonalite and diorite, 

 probably post-Ordovician and pre-Carboniferous, 

 and represented by the granites of Saugus and 

 Dedham, etc.; (3) a "felsitic" group, a complex 

 of felsites, granophyres, tuffs and breccias, of 

 early Carboniferous age, and covering several 

 large areas; (4) a "granitic" group, including 

 granite, quartz porphyry, nordmarkite, etc., repre- 

 sented by the granites of Quincy and Peabody, 

 etc., of Carboniferous age and possibly contem- 

 poraneous with the "felsitic" group; (5) a 

 " basaltic " group, represented by the " Brighton 

 amygdaloid," of Carboniferous age, and (6) a 

 " diabasic " group, comprising hundreds of dikes 

 of Triassic age. There are also some pre-Triassic 

 diabases, of as yet uncertain age. 



Fluidal Gneiss and Contemporary Pegmatites: 



Whitman Ceoss. 



In the Needles Mountain pre-Cambrian area in 

 southwestern Colorado there are several granitic 

 batholiths. One of these, called the Twilight 

 granite mass, is intruded in most intricate fashion 

 in steeply upturned Archean amphibole schists. 



Both gneissic and schistose textures are exhib- 

 ited in the intrusive granite. The former is a 

 fluidal texture originating during the consolida- 

 tion of the granite. Such textures curve in and 

 out among amphibole schist fragments, the sharp 

 angles of which are notable. Where a secondary 

 schistose texture occurs the amphibole schist and 

 granite are both crushed and sheared and it is 

 difficult to determine in certain localities which is 

 the intrusive rock. 



Pegmatite occurs as a phase of the granite in 

 arms penetrating amphibole schist or in relatively 

 small dikes connecting larger gneissose bodies. 

 The transition of the pegmatite into gneissoid 

 granite or granular rock and the absence of peg- 

 matitic dikes cutting the latter show that the peg- 

 matite is practically contemporaneous with the 

 granite. None of these pegmatite masses is more 



than a few inches wide and the minerals are 



those of the biotite granite. 



Pleistocene Geology of the Leadville Quadrangle, 



Colorado: S. R. Capps. 



The work was commenced in 1903 with E. K. 

 Leffingwell, and completed the following summer 

 with the assistance of J. M. Hill and C. A. 

 Kirtley. Of the 950 square miles of the quad- 

 rangle, more than 350 square miles have been 

 glaciated. In this area 36 ancient valley glaciers 

 were studied and mapped. Moraines of two dis- 

 tinct epochs of glaciation, one much older than the 

 other, were found. The ice of the earlier epoch 

 covered approximately the same areas as that of 

 the later one. 



The great terraces near Leadville, which have 

 hitherto been referred to as lake beds, are prob- 

 ably remnants of compound alluvial fans, de- 

 posited as outwash from the older glaciers. This 

 conclusion is based upon the imperfect stratifica- 

 tion of the materials, their lack of lake bed struc- 

 tures, the absence of shore lines, and upon the 

 similarity in structure to present alluvial fans. 

 The terraces also show the same amount of weath- 

 ering as the older moraines, and the topographic 

 relation between the terraces and these moraines 

 is significant. Lower terraces were found which 

 bear similar relations to the moraines left by the 

 last glaciers. The courses of the Eagle River 

 above Redcliff, and of the Arkansas River, near 

 Granite, have been altered as the result of ob- 

 struction by the glaciers. 



Francois E. Matthes, 



Secretary 



At the 216th meeting of the society, held at 

 the Cosmos Club on Wednesday evening, March 

 10, 1909, Mr. Wirt Tassin presented an informal 

 communication on " A Method of Illumination for 

 the Study of Opaque Substances under the Micro- 

 scope," and showed the apparatus for same in 

 operation. 



Mr. F. E. Matthes, on behalf of Mr. R. H. 

 Chapman, gave a brief communication on the 

 Culinan diamond, and showed glass models of the 

 stone in the rough and of some of the larger 

 gems cut from it. 



Regular Program 

 Primary Scapolite in Igneous Rocks: F. 0. Cal- 

 kins. 



In the Philipsburg quadrangle, in western Mon- 

 tana, a thick series of sediments, largely cal- 

 careous, is invaded by batholiths of rocks allied 



