It is easy to state a theory that shall look plausible so long as it is confined to general terms, but when it comes to be worked out in detail it will seem to be more and more difficult and involved at every step.

The Logia hypothesis in fact carries us at once into the very nodus of Synoptic criticism, and, in the present state of the question, must be regarded as still some way from being established.
The problem in regard to St.Mark and the triple synopsis is considerably simpler.

Here the difficulty arises from the necessity of assuming a distinction between our present second Gospel and the original document on which that Gospel is based.

I have already touched upon this point.

The synoptical analysis seems to conduct us to a ground document greatly resembling our present St.Mark, which cannot however be quite identical with it, as the Canonical Gospel is found to contain secondary features.
But apart from the fact that these secondary features are so comparatively few that it is difficult to realise the existence of a work in which they, and they only, should be absent, there is this further obstacle to the identification even of the ground document with the Mark of Papias, that even in that original shape the Gospel still presented the normal type of the Synoptic order, though 'order' is precisely the characteristic that Papias says was, in this Gospel, wanting.
Everywhere we meet with difficulties and complexities.