Geology of California. — Turner. 313 
formation, and apparently interstratified with limestone contain- 
ing Carboniferous fossils, in Calaveras county, are pebbles of dia- 
base. Some diabase is presumably, therefore, of pre-Mesozoic age. 
The western belt of the Calaveras formation contains consider- 
able areas of f ragmental rocks of the diabase and prophyrite series. 
These areas present every evidence of being of the same age as 
the enclosing sedimentary rocks, that is, Carboniferous. (See 
Placerville and Jackson atlas sheets. ) 
On page 437 is described a belt of argillite and limestone that oc- 
curs between Campo Seco and Mokelumne hill. Mr. Mills refers this 
belt to his Lower Mesozoic, apparently on its general lithologic char- 
acter. This is the Western belt of the Calaveras formation al- 
ready' referred to, and the limestone of this belt contains Fnsilina 
cylindrical which has thus far not been found highel' than the 
Permian. 
The Upper Mesozoic group of Mr. Mills is characterized by 
thinly laminated slates and serpentine. The latter rock appears 
to occur chiefly in the lower part of the Upper Mesozoic. Thus 
on page 431, "It is plain, therefore, that in the ascending ser- 
ies the serpentines and the slates which accompany and replace 
them came before the thinly laminated slates, and that the latter 
are at the head of the whole series of metamorphic rocks of the 
Sierra. ' ' 
Northeast of Pence's ranch, in Butte count}-, is a group of 
older sedimentar}' rocks, in the limestone of which are rounded 
crinoid stems, and in the same limestone Productus semi ret iculatns 
and Spirifer Uneatus were recognized by Mr. W. M. Gabb, of the 
State Geological Survey of California. These fossils are char- 
acteristic of the Carboniferous, yet Mr. Mills (page 434), appar- 
ently merely because of the association of serpentine with these 
rocks, "sees no reason to doubt that these limestones with 
accompanying slates, greenstones and serpentines" are of Mesozoic 
age. 
As may be seen on the Jackson geological atlas sheet, soon to 
be published, large amounts of amphibolltc-.schi.sts (part of Mr. 
Mills' Lower Mesozoic greenstones) are included in the area of 
the "Calaveras formation" to the north of Angel's, which is so far 
as known of Paleozoic age. These schists are dynamo-metamor- 
phic rocks which were largely diabase originally and have been 
subjected to the same displacements as the enclosing sedimentary 
