On website FamilySearch.org, this baptism register is identified as "Marriages 1906-1925 with index" under the heading "All Saints Parish (Chicago: S State)". Here is the link to the online register:
This marriage register is a bound book that consists of:
The following is the summary of information about the images in this set:
[The actual marriage register book has register pages that go beyond register page 67 and those pages contain entries beyond 1925, but the images available online stop at register page 67.]
There is a gap in this index. If your immigrant Lithuanian ancestor was married in All Saints church between 26 September 1915 and the end of 1925, the marriage will not be listed in this index. In general, the index pages appear to be very reliable for finding entries on register pages 1-41 (marriages from 1906 through 20 September 1915, when Rev. F. B. Serafinas was the pastor) but the index was not maintained after that for at least 20 years. As an illustration of this situation, refer to the example index page for the "Z" names in the index, which has been annotated with red rectangles to highlight the items of interest.
Typical Index Page in All Saints Lithuanian RC Parish Marriage Register
(red rectangles added to highlight entries identified in description below)
The first 15 entries (surnames of grooms) have indexes to numbers in numerical order from 70 to 258. These are indexes to entry numbers (not page numbers) and they are representative of the reliable entries in this index through 20 Sep 1915. Immediately below that, a new index begins that is indexed to page numbers, and it begins with page 95, which means there has been at least a 20-year gap in the index. The subsequent entries refer to register pages in numerical order (as expected), but there is sometimes an entry with an out-of-sequence page number. Typically that is an "add-in" index entry to a page in the 20-year index gap. On this "Z" index page, there is such an entry (highlighted) that refers to register page 52, and there is also a similar entry above it that refers to register page 83. The entries on this "Z" index page extend to register page 152, which are many years beyond the register pages available for online viewing.
These pages contain the actual entries about the marriages that took place in the parish. Refer to the image below, which is an image of register page 40; this page contains the marriage entry for my maternal grandparents. The format of this register page is typical of all register pages in this marriage register.
The title portion of each 2-page-wide register page has:
The blank after "Annus" was meant to be filled out with the year that applied to the entries on the page. On register page 40, the entry is "1914-1915". The blank after "in Ecclesia" was meant to be filled out with the name of the church (in Latin) in which the marriages on that register page occurred. On register page 40, the entry is "Omnium Sanctorum" (of All Saints). For All Saints church, the typical entry was "Omnium Sanctorum" until register page 42; after that a new pastor arrived and he typically didn't fill in the blank spaces at the top of each register page. [The pages for the initial period prior to the use of the first parish church in mid-1908 have the same designation.] The overall title would be "Registrum Matrimonium in Ecclesia Omnium Sanctorum", which translates to "Register of Marriages in the Church of All Saints", which I would further shorten to "All Saints Church Marriage Register".
Typical Register Page from All Saints RC Parish Marriage Register, 1906-1925 (with example entry)
(red rectangle added to highlight example entry)
The column-heading portion of each 2-page-wide register page contains 11 column headings, with the first 8 being on the left-hand page. The column headings are listed below, with my comments about typical entries:
The main portion of each 2-page-wide register page contains space to record the entries for 7 marriages, with the entry for each marriage first having a row titled "Sponsi" for entries about the groom, followed by a row titled "Sponsae" for entries about the bride.
In general, all of the given names of persons in this register are in Latin (nominative case). With respect to translating the Latin given names in this marriage register:
In this register, the surname appears to be typically written as the actual Lithuanian spelling of the surname, except that the vowels are typically Americanized by omitting any diacritical marks. With respect to Americanizing the vowels, that was only a "slight" corruption because it really didn't cause any loss of information; Lithuanian-speaking people would know where to restore the diacritical marks.