270 W. N. LOGAN 
extension was far beyond that of the Horsetown.* The Jurassic 
beds do not occur in the Puget Sound region, and as they under- 
lie the Horsetown elswhere, it is evident that the Jurassic. shore- 
line at this point must have been at least as far west as the 
present shoreline. 
A second cause for the lack of communication between the 
“two provinces may lie in the position of the ocean currents. 
The Californian currents coming from the west along a line lying 
between the Queen Charlotte Islands and the island of Vancou- 
ver turns south at some notable distance from the coast, and 
after passing Vancouver bears toward the coast and flows.on 
along the Californian province. The North Pacific current which 
flows east closely parallel to the Californian bears northward 
before reaching the Queen Charlotte Islands. Neither of these 
currents, since they do not cross the line separating the two 
provinces, is effective in establishing communication by carrying 
embryonic or larval forms which might under different cir- 
cumstances be brought within their reach. This same distribu- 
tion of ocean currents probably held during Jurassic times, as in 
general, the large land masses in this region, at least, had their 
present distribution. 
The attractive feeding ground furnished by the epicontinental 
sea doubtless exerted its influence to prevent southern migra- 
tion. When later the waters were drawn off the continent the 
accumulation of the great numbers of organisms on the coast 
may have been sufficient to force the migration southward. Or 
perhaps the interval of time was sufficiently long tor some of 
these northern species to have forced their way into the Califor- 
nian province during later Jurassic time. In either case we 
would have in the Upper Jurassic faunas of California a north- 
ern element, and this seems a wel!-established fact. Neverthe- 
less, since this Upper Jurassic fauna has been reported from 
Mexico it is evident that communication was freer between the 
two provinces after the withdrawal of the waters of the epiconti- 
nental sea. And it is very likely that the movement which caused 
tSee map p. 271. 
