Hole 735B nevertheless provides the only detailed lithologic perspective on the lower ocean crust obtained thus far by drilling. The payoff for the drilling lies in deciphering how the deformed, metamorphosed, and repeatedly intruded rocks of the core were emplaced at the ridge axis before all of that took place. Some of the overlapping threads of asymmetry need to be disentangled and the section reconstructed as it originally was. A start on this is made in several chapters in this volume, including our own synthesis.
Hole 735B was successful because it was spudded at a very easy place to drill and because the newly designed hard rock base provided the means to reenter the hole dozens of times. Hole 735B was eventually lost, however, because it was never designed to be exceptionally deep. Thus, a shortcut was taken to facilitate the success of the second half of Leg 118 after nearly a month of little accomplishment. No casing was placed between the hard rock base and the top of the hole. In the end, this decision proved costly since it so severely limited the options for retrieving the pipe that fell into the hole near the end of Leg 176.
Hole 735B was also too far away from the usual paths of JOIDES Resolution to revisit either expeditiously or repeatedly. All the promise of successful drilling portended by Leg 118 was unavailing either to secure funding for site surveys or to schedule renewed drilling until legs with other objectives in the southern oceans could be scheduled around it. Clearly, following up a similar success in the North Atlantic would not have taken 10 years. The additional difficulty now with Atlantis Bank is that the very deepest objective—coring beyond the gabbro section—has to be framed in terms of a completely new hole, whether it is placed right next to the old one, somewhere else on the platform, or even in another ocean. At least two legs of the standard 55-day duration will be required to do this properly. This would be far easier to confront logistically if Atlantis Bank was not so remote. Atlantis Bank is tantalizing because it is so easy to drill; it frustrates because no one else in the drilling community wants to take the ship into the Indian Ocean for very long.
The situation exemplifies the crossroads now facing deep drilling of the ocean crust. Its particular objectives are tied less to geographical locality than to generic types of ocean crust. Success, however, depends either on targeting places that can be drilled easily or figuring out how to drill at difficult places. The latter requires money and drilling time for testing of equipment. Money is sparse, drilling time is in competition with every other program, and truly easy places to drill are very hard to find. For plutonic rocks, we have not yet found another like Atlantis Bank. To follow up Hole 735B at Atlantis Bank or any other location and advance our understanding beyond that gained by coring gabbros for 1508 m will now require a sustained commitment to engineering development, to setting up holes properly at the outset, and to minimizing risk thereafter. To drill deeper, we shall either need to find an equivalent but closer place to drill and start from scratch or return to Atlantis Bank. Wherever we go, we shall need either to return to the location frequently or park a platform there for as much time as is required to complete the project. We will only begin to have such options when two platforms become available for drilling and we start considering drilling objectives in terms of projects rather than legs.