Talwin Morris, Vellum Edition.

The above is my cover of the Vellum Edition Cover variant; The Red Letter Library, Devotional Series, circa 1905, designed by Talwin Morris.
This is the cover for which Mrs. Brown wrote to Blackie asking if the cover device could be explained.

Talwin Morris replied thus:
"Intimate with the base of the Cross is the Cor Sacrum. Attracted by which (in similar form, but insignificant in comparison) are the two smaller hearts of Faith and Hope.
Interwoven with the Cross is the Vesica Piscis, extending within and beyond the Circle of Eternity; in the Centre of which are other five heart forms - having reference to the Cardinal Virtues (with Charity), and corresponding with the five Wounds of Christ.
Continuous with the outline of the Cross itself is the emblem of the Tabula Eucharistae."

Truly, I am not worthy.

Talwin Morris.

The above graphic is my cover of one variant of the designs Talwin Morris produced for the Red Letter Library series of religious ('devotional') titles issued by Blackie in 1903.
Usually bound in leatherette, the texts were printed in black ink with the running headings in red ink, hence the series name.
Talwin produced at least four (known to me) variants, all featuring a Cross, and other common elements.

Talwin responded to a letter written to Blackie & Son by a Mrs. Brown, asking for an explanation of the meaning of the graphic on the vellum edition, which is different to that above, but we can possibly transpose some of the common elements from Talwin's explanation to the above graphic. Possibly.
Talwin's reply is full and complete, and I will give more detail when I cover the graphic of the vellum edition, meanwhile I will list the common elements I believe are used in the graphic above, and my interpretation of the elements that are not common.
Interwoven with the Cross is the Circle of Eternity, within which, and extending beyond, is the Vesica Piscis.
(Although an adapted form of the Vesica Piscis with a circular top.) I don't know why.
The non common elements for which no explanation is known are the kidney bean/poppy seed shape at the base of the Cross which may represent the Sacrum Cor, the two plant-like shoots extending up from the base of the Cross, which may represent the Tree of Life, and the five teardrop forms which may represent the five wounds of Christ.
The teardrop forms appear on other cover and spine designs, similar, but not always exactly the same. Again, I don't know what they are. All suggestions are welcome!
The original cover can be seen here. Click upon the thumbnail for a larger view.
All homage to Talwin Morris.