308 The American Geologist. May, isas 
since the publication of professor Whitnej'S ''Auriferous Gravels 
of the Sierra Nevada," in 1880. 
From most of the published material on the subject one 
gathers the idea that the quartz deposits forming the Mother lode 
occur uniformly in black clay slates, shown b^^ professor Whitney 
to be of Mesozoic age. Mr. Fairbanks is perhaps the first to have 
indicated that the Mother lode fissure does not follow this belt of 
slates at all points. In Tuolumne county it is noted as cutting 
"a knob of granite one thousand feet across." At another place, 
p. 221, Mr. Fairbanks states that "the formation of the Mother 
lode is the final event in the history of these rocks; no dikes inter- 
sect it, and the fissure has broken through all the formations that 
lie in its path.'' 
That the lode occurs in southern Calaveras county, to the 
east of the "Mariposa slates, '* does not seem to have been noted. 
There is a small amount of black clay slate of unknown age at 
Angel's in one of the mines, but the country rock there is a green 
amphibolite-schist and the main belt of black slates lies a mile or 
more to the west. The United States Geological Survey has 
obtained additional evidence of the Mesozoic age of these slates 
within the past two years. At the Texas ranch, which lies two 
and a half miles southwest of Angel's, and to the west of Angel's 
creek, Aucella and ammonites have been found, and an ammonite 
was obtained from Mr. J. W. Bliss, said to have been found in 
the black slates about two miles west of Angel's on a bran'^^h of 
Cherokee creek. 
On page 219 Mr. Fairbanks makes^this statement: "The 
evidence of fossils recently found in limestone in Tuolumne and 
CalaA^eras counties is supposed to favor the Carboniferous rather 
than the Jurassic. The fossils are few and quite fragmental, and 
*The Mesozoic black clay slates of the gold belt containing Aucella, 
ammonites, and belemnites, have been designated '"Mariposa slates" on 
the forthcoming maps of the United States Geological Survey. 
There are two main belts of rocks of this series, an eastern belt contain- 
ing much of the Mother lode, and a western belt extending from Folsom 
to Salt Spring valley west of the Bear mountains, and further south. 
The western belt contains numerous small quartz veins, but these have 
not yet been shown to be highly auriferous. 
The locality called Wilkinson's ranch in Whitney's Auriferous 
Gravels, p. 37, near White Rock station in Sacramento county, is on this 
western belt of slate. According to professor Whitney, an ammonite 
was obtained there. The writer found fossil belemnites in Salt gulch 
about two miles northeast of Campo Seco in Calaveras county, and what 
may also be a belemnite fragment in the clay slates that cross the 
Tuolumne river a little east of Lagrange. 
