June 12, 1896 ] 



SCIENGK 



879 



pinus Astragalus PotentUla Horkelia and many 

 more. Equally remarkable and interestingly 

 suggestive is the fact that certain trees, shrubs 

 and herbaceous plants, long known as ex- 

 tremely rare, or quite local, on the mainland 

 shores — such as Pinus Torreyana, Malacothrix 

 incana and Leptosyne gigantea — have more re- 

 cently been found to occur in the most luxuri- 

 ant abundance on these outlying islands. Their 

 rare occurrence on the continental shore is at 

 just those points where their seeds would natur- 

 ally land if drifted across from the islands. The 

 conclusion is unavoidable that, in so far as 

 these belong to the continental flora, they have 

 been given to it from the islands, these latter 

 being their original habitat. In a word, the 

 character of this insular flora departs from al- 

 most all known rules, and in so far that, viewed 

 as to their flora, the whole group seem like 

 oceanic islands crowed over against the border 

 of a continent. 



The land mammals of the islands were dis- 

 cussed by Dr. Edgar A. Mearns, who enumer- 

 ated, in addition to the genus Homo, twelve 

 genera and upwards of twenty species of native 

 terrestrial mammals which are at present known 

 to inhabit the islands off' the coasts of southern 

 and Lower California, and alluded to others 

 remaining to be described by the energetic and 

 adventurous naturalist, Mr. Walter Bryant, 

 whose explorations of Guadalupe, Cedros, Es- 

 perito-Santo and the other islands off" the Pa- 

 cific and Gulf coasts of Lower California are 

 so well known to naturalists. 



Dr. Mearns described and exhil^ited speci- 

 mens of a new mouse (Peromyscus) and a new 

 kangaroo rat (Dipodomys) recently collected on 

 Tiburon Island, in the Gulf of California, by 

 Mr. J. W. Mitchell, who accompanied Prof. 

 McGee on his latest expedition. He also re- 

 marked upon the close relationship existing be- 

 tween the island mammals as a whole and those 

 of the neighboring mainland, insomuch that 

 their origin from the latter could be readily 

 traced in each instance, though none are actu- 

 ally identical, thus furnishing a plain and strik- 

 ing illustration of the evolution of species. 



Of domestic animals, the goat, sheep, cow, 

 donkey, dog, cat and house rat have been in- 

 troduced on one or more of the islands, and, in 



several instances, some of them bid fair to de- 

 stroy the native fauna or flora of certain 

 islands. 



In the discussion which followed this paper. 

 Dr. C. Hart Merriam added a genus to the 

 known mammal fauna of these islands, a 

 species of the little spotted skunk (Spilogale) 

 having been taken on Santa Catalina Island, 

 one of the Santa Barbara group. 



A skin of the Western Desert mule deer, 

 (called '£iMTo'), was sent to the Society for ex- 

 amination by Prof. W J McGee, who obtained 

 the specimen in the Sierra Seri Souora. Dr. 

 Mearns had also found this deer on the Western 

 desert tract, both east and west of the Colorado 

 river. 



Mr. Harry C. Oberholser spoke briefly of 

 the birds of the island, calling attention to the 

 number of subspecies which were evidently 

 descended from continental forms. 



F. A. Lucas, 



Seci'etary. 



GEOLOGICAL SOCIETY OF WASHINGTON. 



At the 50th meeting of this Society held May 

 27th, the last meeting until next fall, the fol- 

 lowing papers were read and discussed: 



Texture and Structure of Soils : By Peof. 

 Milton Whitney, of U. S. Department of 

 Agriculture. The following forces are usually 

 spoken of as the principal ones in the disintegra- 

 tion of rocks and the formation of soils, 1. 

 Changes of temperature. 2. Moving water or 

 ice. 3. Influence of vegetable or animal life 

 (shades the land; admits air; solvent action of 

 the roots; chemical action of decaying organic 

 matter, earthworms and bacteria). 4. Chemi- 

 cal action of air and water. 5. Oxidation and 

 hydration. Attention was called to the fact 

 that all of these forces, except the solvent action 

 of water and hydration, are largely superficial 

 and would not act at any considerable depth. 

 They certainly can not explain the disintegra- 

 tion of rocks to a depth of 50 or 75 feet as is 

 seen in the crystalline areas at the south. 

 If the solvent action of water has been the 

 main cause of the disintegration of rocks, 

 then 50 per cent, of the rock must have 

 been dissolved and carried away. If the 



