The immense Bay of Mont St. Michel, at low water, is a stretch of bare sand more than three hundred square kilometres in extent, but it is completely covered and converted into a great tranquil gulf by the rising tide.
Croisic
At Croisic, at the mouth of the Loire, there is a 5.16 metre rise of the tide, which around the Breton coast-line varies as follows:
| Port Navalo, Morbihan | 4.72 |
| Lorient | 4.60 |
| Concarneau | 4.68 |
| Douarnenez | 6.16 |
| Brest | 6.42 |
| Ouessant | 6.38 |
| Roscoff | 8.22 |
| Ile Brehat | 9.90 |
| St. Malo | 11.44 |
| Iles Chausey | 11.74 |
| Mont St. Michel | 12.30 |
The aspect of the region round about Dol, in the north, is that of a little Holland, with its flats and windmills and its cultivated ground protected from the sea by a rim of downs and dikes. It is not so very great an expanse that follows these outlines, but the likeness is one to be remarked. To the westward lie the jutting rocks and capes, beyond which are the isolated islands of Ouessant and its fellows, and all around the coast extend landlocked bays and harbours sheltering the great fishing ports of Douarnenez and Concarneau and the commercial ports of St. Malo, Morlaix, Brest, Lorient, and Vannes.
From a military and strategic point of view the whole northwest coast of France, from the mouth of the Loire through Brittany and Normandy, is exceedingly well protected, with a great port and base of supplies both at Brest in Brittany and at Cherbourg in Normandy.