Erratic Cambrian Fossils.— Woodworth. 945 
tion, perhaps one per cent. of the pebbles in the osseous con- 
glomerate are of chert. 
Immediate origin of the Chert: The immediate source of these 
fossiliferous Cambrian pebbles is apparently to be found in the 
coarse sands and gravels underlying the Neocene formations. 
The age of these beds has not yet been definitely settled: They 
lie, unconformably, by slight erosion of their upper surface, 
below the marine Neocene or osseous conglomerate, and they 
overlie, without recognizable unconformity, the plant bearing 
Cretaceous beds which include the Gay Head lignites. On 
account of this apparent continuity of deposition succeeding the 
Cretaceous beds, the sands and gravels may tentatively be con- 
sidered of the same age. No fossiliferous pebbles have as yet been 
PLEISTOCENE. 
( Green sand. 
N EOCENE. 
? Osseous conglomerate. 
White 
e Sands 
= and 
2 Y 
s Clays. 
Leaf beds. 
Lignites. 
_ Fie. 3. Correlation section of the strata involved in the Gay Head dislocation, show - 
ing position of osseous conglomerate, and Cretaceous gravels. 
found in the exposures of these Cretaceous sands and gravels, 
although they are probably present in these beds, as is shown by 
the consideration of the origin of the detritus in the osseous 
conglomerate. 
The detritus of the osseous conglomerate appears to have been 
derived as follows: Sometime after the deposition of the Creta- 
ceous sands, clays and gravels, the surface of this formation was 
exposed to ablation in a manner to assort out and carry further 
down the coastal slope much of the finer material, leaving behind 
after a short carriage. a stratum of coarse gravel of the thickness 
previously described. That this quartz pebble conglomerate at the 
base of the identified Neocene was derived from the underlying Cre- 
taceous beds by asifting process like that just appealed to, and not 
