def find_primary_lithology(tokens, lithologies_dict):
    """Find a primary lithology in a tokenised sentence.

    Args:
        v_tokens (iterable of iterable of str): the list of tokenised sentences.
        lithologies_dict (dict): dictionary, where keys are exact markers as match for lithologies. Keys are the lithology classes.

    Returns:
        list: list of primary lithologies if dectected. empty string for none.

    """
    keys = lithologies_dict.keys()
    for x in tokens:
        if x in keys:
            return lithologies_dict[x]
    return ''
