The environment prevalent in modern marine seas limits the distribution of biologic assemblages in those seas. Since conditions of the environment can only be inferred for seas that no longer exist, it is obvious that comparisons with the seas of to-day are important in developing criteria by which to reconstruct conditions of environment for ancient seas.
Blaine and Dog Creek deposits include strata from which the remains of both plants and animals have been recognized. These biologic assemblages have been studied for evidence of the environment prevalent in Blaine and Dog Creek seas. It is observed that the thallophyte floras and invertebrate faunas were characteristic assemblages of those ancient seas. Accordingly, their fossil evidences are important in reconstructing ecological history for Blaine and Dog Creek seas and deposits.