ACADEMY OF SCIENCES. 183 



the Ostrea edulis of England, which when transplanted to the oyster beds of the 

 Mediterranean, takes on some of the characteristics of the native Mediterranean 

 species (0. cochlear). These observations are not without interest, from their 

 bearing on the variation of species, and the various doctrines of evolution and 

 selection of organic forms. 



Dr. Blake read a short communication on some diatoms he had 

 collected at a hot spring in Pueblo Valley, Humboldt county, Ne- 

 vada, where they were growing in water the temperature of which 

 was 163 deg. F. 



The forms were very abundant, a small portion of the mud not larger than a 

 pin's head, containing many hundred individuals, amongst which could be rec- 

 ognized more than fifty different species. Tlie most interesting point con- 

 nected with the discovery of these diatoms, was their almost perfect identity 

 with the species found in beds of infusorial earth in Utah Territory. So close 

 was their identity, that there can be but little doubt tliat the Utah beds must 

 have been formed in an inland sea, whose temperature was probably about the 

 same as that of the water of the Pueblo spring. The fact that these diatoms 

 can grow in such abundance in water of so high a temperature, affords an ex- 

 planation of the total absence of every other form of organized beings in the 

 infusorial beds, as such an elevated temperature would be totally incompatible 

 with the existence of every other form of living beings. The time at which 

 these infusorial beds were deposited was probably during the ]\liocene period' 

 as we have evidence that at that period Spitzbergcn and other Arctic regions 

 had a temperature some fifty or sixty degrees above that of their present 

 climate. 



He also read an article on Prismatic Dolerite, an interesting 

 form of volcanic rock found near Black Rock, Nevada. 



Columnar Dolerite. 



The specimens of this rock were presented to the Academy some three or four 

 meetings since, and I then stated that I believed they were examples of the 

 crystalizcd form of some volcanic rock, most likely related to basalt. Not 

 having examined them particularly, and the surface of the mineral being 

 much weathered, I gave a specimen to iNIr. Durand, who at the next meeting 

 of the Academy presented a memoir on the subject, in which he stated that 

 the crystal was Amphibole. Xot, however, being satisfied that my first opinion 

 was incorrect, I prepared a thin section of one of the crystals, or crystalline 

 prisms, and looked at it through the microscope. This section I now present 

 to the Academy, and even an examination of it with the naked eye sufiices to 

 prove that it is a compound rock, made up of heterogeneous substances, em- 

 bedded in a dark greenish matrix. With the microscope we detect crystals of 

 augite, nephiline or ]abradorite,and titanite. I believe the transparent crystals 



