//server code

        var jsonData = new
        {

            rows =
            (from bathymetrie in bathymetries

             select new
             {
                 count = bathymetries.Count,
                 Id = bathymetrie.Id,
                 date = (bathymetrie.displayedDate != null) ?
        bathymetrie.displayedDate.ToString() : ""
             }).ToArray()
        };


  //client code

 success: function (data) {

            bathyms = "{";

            for (var i = 0; i < data[1].count; i++) {

                bathyms += el[i].Id + " : " + el[i].date;

                alert(el[i].Id);
                alert(el[i].date);
                console.log(el[i].date);

                if (i != data[0].count) {

                    bathyms += ",";
                }

            }
            bathyms += "}";
        }

for (var i = 0; i < data.rows.length; i++) {
    var element = data.rows[i];
    // use element.Id, element.count and element.date

public class Data
{
    public int Id { get; set; }
    public int Count { get; set; }
    public string Date { get; set; }
}

public ActionResult GetJson()
    {
        Data[] a = new Data[2];
        a[0] = new Data() { Count = 10, Id = 1, Date = "2/19/2014" };
        a[1] = new Data() { Count = 20, Id = 2, Date = "3/19/2014" };

        return new JsonResult() { Data = a };
    }

<script src="~/Scripts/jquery-1.10.2.min.js"></script>
<script>
    function submitForm() {
        jQuery.ajax({
            type: "POST",
            url: "@Url.Action("GetJson")",
            dataType: "json",
            contentType: "application/json; charset=utf-8",
            success: function (data) {
                $.each(data, function (key, value) {
                    alert(value.Id + ' ' + value.Count + ' ' + value.Date);
                });
            },
            failure: function (errMsg) {
                alert(errMsg);
            }
        });
    }
</script>

<input type="button" value="Click" onclick="submitForm()" />

success: function (data) {
            $.each(data, function (key, value) {
                alert(value.Id + ' ' + value.Count + ' ' + value.Date);
            });