The Problem:

TLE Small Dome disc installation fails on OSX.

The Solution:

On the disc, right click on Install The Layered Earth Small Dome (which is .mpkg file) and then go to Show Package Contents.

After that go to Contents/Resources to find 2 .pkg files - The Layered Earth Small Dome.pkg and The Layered Earth Essential Data.pkg .

If you double click these files you get to install those particular components (since they correspond to the app and CacheData, respectively).

First, install the The Layered Earth Small Dome.pkg, then The Layered Earth Essential Data.pkg .