AND DISTRIBUTION OF TRILOBITES. 279 
the east as on the western side of the Baltic, on the coasts of 
ivonia, Ingermannland and in Karelia. EKichwald (Iter per 
ngriam, Casani, 1828), Pander (Contributions to the Geology of 
Russia. Petersburg, 1830), and, in the most recent period, Bla- 
ius (Journey through Russia, 1843, vol. i.), have described 
che same succession of strata in the neighbourhood of Reval and 
Petersburg ; it only deviates from it in so far that the upper 
elay-slate is wanting, and a blue clay forms the basis of the lower 
sandstone instead of the crystalline slate rock, a peculiarity which 
would have been considered incredible some years ago. The 
sandstone is not so poor in fossils as it is in Sweden, but some 
strata are found to consist almost solely of very remarkable mi- 
ute Brachiopoda (the Ungulites of Pander), even the cement- 
ng medium being wanting. I am not acquainted with any fos- 
sils from the alum-slate which rests upon the sandstone. 
There are some islands in the Baltic situated between the 
ussian and Swedish shores, viz. Osel near the Russian, and 
land and Gothland near the Swedish shore. The two former, 
Osel and Oland, are formed of the Trilobite and Orthocera- 
tite limestone ; on Oland, the other subdivisions have likewise 
deen found at the base. On Gothland, on the other hand, we 
aeet with a fifth formation, a limestone abounding in fossils, 
which Hisinger already looked upon as a younger link of the 
ansition rocks. It has not yet been positively ascertained 
vhether a representative of it is also to be found in Russia. 
the limestone alluded to of Gothland rests upon a sandstone 
which contains two Brachiopoda (Orthis pecten, Terebr. reticu- 
aris), which are frequent in the clay-slate of West Gothland. 
hese five subdivisions of the northern transition limestone may 
be characterized by Trilobites. The alum-slate by the genera 
Paradoxides, Olenus and Battus (pisiformis) ; this slate, on the 
other hand, is entirely deficient in fossils in Russia. The prin- 
“ipal limestone contains the genera Asaphus, Brong. emend., 
Menus, Dalm. emend., and Amphion, Pand. The following ge- 
iera are found with equal frequency on both sides of the Baltic: 
A. expansus, Illenus crassicauda, more rarely A. armadillo: 
facetted Trilobite, viz. Phacops sclerops, Dalm.., is likewise met 
vith throughout the whole northern European transition forma- 
tion. There are only two species which, according to Dalman, 
€ common to both the upper strata of this limestone and to the 
lates of the Méseberg, viz. Phacops mucronatus and Trinucleus 
