You guys know that I hate to be a contrarian, but I don't think that CBM's original Biarritz concept was based upon any of these holes thus far mentioned. The Chasm hole at Biarritz may have given CBM inspiration for later holes, but not for the original Biarritz concept. Likewise, the 16th green at North Berwick may have been an inspiration or even a model green for CBM, but not for the original Biarritz concept.
So far as I can tell, the original Biarritz concept was based on a different hole at Biarritz, likely one down by the water in the Chambre d'Amore. CBM discussed the 'inspiring' hole at Biarritz in a June 20, 1906 NY Sun article about his recent trip abroad:
"The idea for one hole comes from Biarritz. The hole in question is not a good one, but it revealed a fine and original principle that will be incorporated in my selection." No mention of the famous chasm --the description of the hole as "not very good" would seem an incongruous reference if he was referring to the famous Chasm!
CBM expanded on the description later that year in his article on ideal holes in Outing Magazine where he provided a sample listing of 18 holes:
"15. 210 yards. Suggested by 12th Biarritz making sharp hog back in the middle of the course. Stopping thirty yards from the hole bunkered to the right of the green and good low ground to the left of the plateau green." Again no mention of the famous Chasm. Rather, CBM described a "sharp hog back" in the middle of the course [hole] ending 30 yards short. And the green is a plateau. Nothing about a double plateau or a dip in the green.
H.J. Whigham repeated this early understanding in 1913 when describing the inspiration for Piping Rock's Biarritz:
"There is a Biarritz hole of about 220 yards which is new to this country and is one of the best one-shot holes in existence. There is a hog's back extending to within thirty yards of the green and a dip between the hog's back and the green." Again, nothing about a chasm. And nothing about a double plateau green. Rather the play is over a "hog's back" which is apparently the first plateau. Then there is the dip which 30 yards before the actual green.
Here is an early schematic of the Le Phare course at Biarritz.
The schematic is undated, but judging by the areas with contour lines, I believe the schematic may have been created by Dunn prior to the expansion to 18 holes in circa 1892. The hole I suspect was the Biarritz is, as CBM suggests, the 12th hole. The contour lines indicate that there was a ridge or "hog back" running up the middle of the hole, and that the hog back looks like it ends approx 30 yards short of the green.
Note that by the time this map was created the "Chasm" had already been reduced to a 90 yard hole. The 12th measured 300 yards, but recall that CBM did not like the hole as it was, and was only borrowing the strategy of the hog back, dip, and plateau green.