What is in this category we call weird fiction. My thought is that perhaps it is the very mandanity of the bits of our world that are, upon being numbered, the source of unease. The crumbs of our lives if noticed are the merely, the immanent, and -- upchuky. Rather than get into a discussion of the immanent, let me quote Machen in one of his books.
The House of Souls (1922) has a plot line involving an elderly relative who receives strange packages.
'[S]he began to have the things through the post.'
'Things through the post! What do you mean by that?'
'All sorts of things; bits of broken bottle-glass, packed carefully as if it were jewellery; parcels that unrolled and unrolled worse than Chinese boxes, and then had "cat" in large letters when you came to the middle; old artificial teeth, a cake of red paint, and at last cockroaches.'
'Cockroaches by post! Stuff and nonsense; your aunt's mad.'
'Edward, she showed me the box; it was made to hold cigarettes, and there were three dead cockroaches inside. And when she found a box of exactly the same kind, half-full of cigarettes, in uncle's great-coat pocket, then her head began to turn again.'
Darnell groaned, and stirred uneasily in his chair, feeling that the tale of Aunt Marian's domestic troubles was putting on the semblance of an evil dream....
It is in this same book that we find another elaboration, of horror, as sin. This interestingly is apparently the opposite of what I mention above:
'I think I must reply to your question by another. What would your feelings be, seriously, if your cat or your dog began to talk to you, and to dispute with you in human accents? You would be overwhelmed with horror. I am sure of it. And if the roses in your garden sang a weird song, you would go mad. And suppose the stones in the road began to swell and grow before your eyes, and if the pebble that you noticed at night had shot out stony blossoms in the morning?
'Well, these examples may give you some notion of what sin really is.”
The above excerpt suggests transcendence, the reaching beyond, is the source of terror. Yet, perhaps the problem is confusing that which is really immanent, FOR that which is superficially transcendent. For you see, the above example, singing flowers say, is not really the fresh, the new, an unknown edge, (which transcendency suggests) but merely rearranging the ordinary. Birds sing, flowers bloom; put them together and you have nothing which is really, original. If I am correct, Machen is not.