272 ^ir N. Yermolojf — Diatom Earth in California. 



" I believe that the diatoms, or the marine species of the Monterey 

 group, are, or were, northern forms, and lived in the cooler waters 

 of the North Pacific of the Miocene, and were brought south by the 

 ocean currents of the time, and were trapped and impounded in 

 such favourable places as wove found along the Pacific coast of the 

 period. 



" Such favourable places were local, and more or less land-locked, 

 or protected areas of the sea, free from sedimentation from the land, 

 and where the surface waters of the sea were free to enter and 

 escajDe, but where they were detained long enough to lose their con- 

 tents of northern forms under conditions of temperature too high 

 to permit their survival. It appears to me that the dej)osits of 

 diatomaceous strata, as they are known in California, are all more 

 or less local, and in their occurrence and distribution conform to this 

 idea. 



" I have also imagined that the climatic conditions of the coast 

 in middle Miocene times were different from those before and after, 

 for there is a well-known change in the character of the sediments 

 of the Miocene, those of the middle being largely organic, and those 

 of the lower and upper Miocene being generally coarse detrital 

 matter in which the organic contents are inappreciable. 



" It may be that physiographic changes in the continental border 

 and in the ocean currents could have brought about these differences 

 in sediments, but there are certain established facts that point to 

 great climatic changes during Miocene times." — A. S. W. 



The siliceous remains in the fossil deposit of Lompoc belong to 

 two main and dominating groups of organisms, Dictyochideae and 

 Diatomacese. The deposit contains also a few Radiolaria, some 

 siliceous sponge-spicules, and a few remains of Litliasteriscus . 



The Dictyochideae are very numerous, in fact nearly as numerous 

 as the Diatoms. This is remarkable and rather peculiar, because, 

 although the genus Dictyocha has as a rule a very wide distribution, 

 being present in nearly all fossil Diatomaceous deposits, yet it 

 generally does not appear in other deposits in such dominating 

 numbers as in Lompoc. Thus it is present in the fossil deposits 

 of Richmond, Va., of Simbirsk, Mors, Oran, Oamaru, Sendai, and 

 others ; it is also observable in the Baltic (Kiel), and even in the 

 Diatomaceous Oozes of the Antarctic Ocean as collected by H.M.S. 

 Challenger at a depth of 1,950 fathoms. Dictyocha is, however, 

 absent from the Polycystinous earths of Barbados. 



In Lompoc Dictyocha is represented by three species, Dictyocha 

 gracilis Ehr., D. speculum Ehr., and D. fibula Ehr. The first two 

 species are abundant, but the third is rather scarce. D. gracilis 

 Ehr. is also present in other Califoruian deposits, for instance, in 

 Los Angeles ; but it is much less numerous than in Lompoc. 



The number of species of Dictyocha, as described by Kutzing, 

 is about thirty-five. Some of the fossil deposits, such as those of 



