The emphasis of data organisation on the specification, design and implementation of large systems raises the question whether data abstraction may be applied to programming languages designed before the widespread use of such techniques. The data abstraction facilities available in FORTRAN 77 are considered, and it is shown that encapsulation is possible for simple data structures. An abstract array data structure is pecified and further refined to allow the definition of iterators. An example of this structure is implemented in FORTRAN 77. The introduction of a series of abstractions is thus made possible, which facilitates structured development and efficient maintenance.