390 Scientific Intelligence. 



while those at considerable depths cooled slowly and became 

 wholly crystalline in texture. 



That all the Washoe regions are of Tertiary age. 



That the so-called granular diorite, diabase, and augite-andesite 

 are identical and belong to the same geological body ; that the 

 porphyritic diorite and hornblende-andesite are identical, and 

 should bear the latter name ; that the so-called mica-diorite is 

 identical with the later-hornblende-andesite ; that the quartz- 

 porphyry resolves itself into both dacite and rhyolite; that the 

 later-diabase and the basalt are one in rock, the former known as 

 a dike and the latter in flat-topped masses. 



That the Comstock lode occupies a fissue along a line of fault- 

 ing in a rock of Tertiary age, and cannot be considered as a con- 

 tact vein between two different rock-masses. 



The facts from the great sections of Washoe rocks so carefully 

 investigated are of fundamental importance to petrography. As 

 far as igneous rocks are concerned, they seem to demolish the 

 system of rock-classification now most popular; for, taking out the 

 distinctions of earlier and later • and that of granitoid, micro- 

 crystalline and glass-bearing, among rocks and groups of rocks, 

 the system goes to pieces, and the definition of species or kinds 

 among rocks will have to fall back, with some exceptions, on the 

 reasonable ground of mineral constitution irrespective of age and 

 texture. J. d. d. 



2. A crystallographic Study of the TMnolite from lake 

 Lahontan ; by Edward S. Dana (Bulletin of the U. S. Geol. 

 Survey, No. 12). — The calcareous tufas of Lake Lahontan, the 

 great Quaternary lake of northwestern Nevada, were called 

 thinolite by King in his Report of the Survey of the 40th Par- 

 allel, in allusion to the fact that they were a shore deposit (Si's, 

 shore). Of these tufas a certain limited portion is crystalline in 

 character, and a study of its forms, as remarked more particu- 

 larly later, led Mr. King to the conclusion that it was a pseudo- 

 morph after the mineral gay-lussite ; and he bases his explanation 

 of the history of the lake upon this hypothesis. The relations 

 of the tufas of Lake Lahontan have been since then thoroughly 

 studied by Mr. I. C. Russell. He shows that there are three dis- 

 tinct varieties, the lithoid or stone-like, the thinolithic, or crys 

 talline and the dendritic ; these were deposited at different stages 

 in the Lake's history in the order named. The chief interest at- 

 taches to the crystalline variety, or thinolite proper, and it is to 

 the description of this that the Bulletin No. 12 is devoted. It is 

 found well developed at a number of different points in the 

 Lahontan basin, conspicuously about Pyramid Lake, and outside 

 of it in that of Mono Lake ; where best exposed it forms a layer 

 of interlacing crystals six or eight feet in thickness. Chemically 

 the thinolite consists of almost pure calcium carbonate. As re- 

 gards general aspect, many varieties are found, from the open, 

 delicately porous form, skeleton-like in character, to that which 

 is firmly compact and has a smooth exterior. The form of the 



