How to define a type holding an array of arrays?

With GraphQL-ruby I want to define a type for a field that holds data in the following structure:

[
  ["2016-06-07", 14134.84],
  ["2016-06-08", 14134.84],
  # ...
]

How would I go for this? I tried

module Types
  class PerformanceDataType < Types::BaseObject
    field :assets, [[Types::AssetType]], null: false
    # ....
  end
end

module Types
  class AssetType < Types::BaseObject
    field :date, String, null: false
    field :value, Float, null: false
  end
end

I am not using that data yet so I can't say if it works, but it feels too unspecific. Generating the schema didn't throw any errors.

We ended up doing it like follows:

# innerArrayType.rb

module Types
  class InnerArrayType < Types::BaseObject
    field :first_value, GraphQL::Types::ISO8601Date, null: false
    field :second_value, Types::DecimalType, null: false
  end
end

# someOtherType.rb

module Types
  class SomeDataType < Types::BaseObject
    field :desiredType, [Types::InnerArrayType], null: false
  end
end

I guess the takeaway is that on the lowest level, an array must be defined using Types::BaseObject.