julia> A = rand(1:9, 10, 7)
10×7 Matrix{Int64}:
1 3 5 3 5 7 5
4 2 3 8 5 7 7
8 3 6 7 6 5 1
6 2 7 6 9 9 8
3 8 6 8 5 9 8
6 4 6 9 4 4 4
2 6 1 9 5 8 6
6 4 5 4 8 9 7
1 8 3 6 4 7 8
9 3 9 6 8 4 4
julia> B = rand(1:9, 10, 7)
10×7 Matrix{Int64}:
5 1 6 8 6 3 8
4 6 2 9 7 4 4
4 7 5 5 3 7 3
3 3 5 6 3 7 6
4 3 6 1 1 7 8
4 4 2 1 3 3 5
6 4 5 2 1 8 2
4 6 9 8 4 2 4
6 7 5 1 9 6 6
2 9 5 3 5 2 6
julia> C = cat(A, B, dims=3)
10×7×2 Array{Int64, 3}:
[:, :, 1] =
1 3 5 3 5 7 5
4 2 3 8 5 7 7
8 3 6 7 6 5 1
6 2 7 6 9 9 8
3 8 6 8 5 9 8
6 4 6 9 4 4 4
2 6 1 9 5 8 6
6 4 5 4 8 9 7
1 8 3 6 4 7 8
9 3 9 6 8 4 4
[:, :, 2] =
5 1 6 8 6 3 8
4 6 2 9 7 4 4
4 7 5 5 3 7 3
3 3 5 6 3 7 6
4 3 6 1 1 7 8
4 4 2 1 3 3 5
6 4 5 2 1 8 2
4 6 9 8 4 2 4
6 7 5 1 9 6 6
2 9 5 3 5 2 6
Also see the [A ;;; B] syntax which is relatively new.